Pellicle Attachment Apparatus

ABSTRACT

Tooling for a mask assembly suitable for use in a lithographic process, the mask assembly comprising a patterning device; and a pellicle frame configured to support a pellicle and mounted on the patterning device with a mount; wherein the mount provides a releasably engageable attachment between the patterning device and the pellicle frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/572,156, filed Sep. 16, 2019, which is a continuation of U.S. patentapplication Ser. No. 15/526,639, 371(c) Date May 12, 2017, which is aU.S. National Stage Entry of International Application No.PCT/EP2015/076688, filed Nov. 16, 2015, which claims benefit of U.S.application No. 62/080,561, filed Nov. 17, 2014, U.S. application No.62/108,348, filed Jan. 27, 2015, U.S. application No. 62/110,841, filedFeb. 2, 2015, U.S. application No. 62/126,173, filed Feb. 27, 2015, U.S.application No. 62/149,176, filed Apr. 17, 2015 and U.S. application No.62/183,342, filed Jun. 23, 2015, which are all incorporated herein inits entirety by reference.

FIELD

The present invention relates to an apparatus. The apparatus may be usedin connection with a pellicle for a lithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine constructed to apply a desiredpattern onto a substrate. A lithographic apparatus can be used, forexample, in the manufacture of integrated circuits (ICs). A lithographicapparatus may for example project a pattern from a patterning device(e.g., a mask) onto a layer of radiation-sensitive material (resist)provided on a substrate.

The wavelength of radiation used by a lithographic apparatus to projecta pattern onto a substrate determines the minimum size of features thatcan be formed on that substrate. A lithographic apparatus that uses EUVradiation, being electromagnetic radiation having a wavelength withinthe range 4-20 nm, may be used to form smaller features on a substratethan a conventional lithographic apparatus (which may for example useelectromagnetic radiation with a wavelength of 193 nm).

A patterning device (e.g., a mask) that is used to impart a pattern to aradiation beam in a lithographic apparatus may form part of a maskassembly. A mask assembly may include a pellicle that protects thepatterning device from particle contamination. The pellicle may besupported by a pellicle frame.

It may be desirable to provide an apparatus that obviates or mitigatesone or more problems associated with the prior art.

SUMMARY

According to a first aspect of the invention there is provided apellicle attachment apparatus comprising a support structure configuredto support a pellicle frame, and a pellicle handling system configuredto place the pellicle onto the pellicle frame, wherein the apparatusfurther comprises actuators configured to provide relative movementbetween the pellicle frame and the pellicle before the pellicle isplaced on the pellicle frame.

The actuators allow alignment between the pellicle frame and thepellicle to be achieved before the pellicle is placed on the pellicleframe, thus allowing accurate positioning of the pellicle relative tothe pellicle frame.

The actuators may be configured to move the support structure, and thusthe pellicle frame, relative to the pellicle.

The pellicle handling system may comprise support arms which areconfigured to hold the pellicle.

Each support arm may include a conduit configured to deliver a vacuum toa foot of that arm.

The foot may be dimensioned to receive a portion of a border of thepellicle.

The support arm may extend downwardly from a connector arm which extendsfrom a frame of the pellicle handling system.

The connector arm may include one or more leaf springs which allow theconnector arm to move in a generally vertical direction.

Adjustable end stops may project from the pellicle handling system frameand prevent downward movement of the connector arm beyond apredetermined position.

Bellows may extend between the support arm and the pellicle handlingsystem frame, the bellows connecting the conduit in the support arm to aconduit in the frame.

The support structure may include windows positioned to allow pellicleborder edges and/or pellicle frame edges to be visible from an oppositeside of the support structure.

Imaging sensors may be provided on one side of the windows and areconfigured to look through the windows to view the pellicle border edgesand/or pellicle frame edges on an opposite side of the window.

Alignment marks may be provided on the windows

The pellicle attachment apparatus may further comprise arms which areconfigured to press downwardly on the pellicle after it has been placedon the pellicle frame, thereby holding the pellicle on the pellicleframe during curing of glue at an interface between the pellicle and thepellicle frame.

Each arm may be provided with a weight. Downward pressure applied by thearm to the pellicle may be determined by the heaviness of the weight.

Each arm may include a downwardly extending finger which is configuredto press against the pellicle

The finger may be laterally moveable relative to other parts of the arm.

Each arm may extend from a support frame and include a portion which ismoveable in a generally vertical direction relative to the supportframe.

Each arm may include end stops which limit movement of the moveableportion of that arm relative to a fixed portion of that arm.

According to a second aspect of the invention these is provided apellicle frame attachment apparatus configured to receive a patterningdevice and a pellicle assembly comprising a pellicle frame and apellicle, the pellicle attachment device comprising manipulatorsconfigured to operate an engagement mechanism of a sub-mount provided ona pellicle frame, wherein the manipulators project through or projectfrom openings provided in a partition which separates a pellicleassembly receiving controlled environment from other parts of thepellicle frame attachment apparatus.

The partition includes windows positioned to allow pellicle borderedges, pellicle frame edges and/or alignment marks on the patterningdevice to be visible from an opposite side of the partition.

Imaging sensors may be provided on one side of the windows. The imagingsensors may be configured to look through the windows to view thepellicle edges, pellicle frame edges and/or alignment marks on thepatterning device.

Alignment marks may be provided on the windows.

The manipulators may comprise pins connected to an actuator, theactuator being configured to move the pins in a generally verticaldirection.

The pins may be moveable relative to a pair of hooked arms.

The pair of hooked arms may be connected to an actuator. The actuatormay be configured to move the hooked arms in a generally horizontaldirection.

The pair of hooked arms may be fixed to the partition, the actuatorbeing configured to move the partition and the pair of hooked arms inunison.

An additional pin may be provided, the additional pin being movable inthe generally vertical direction relative to the moveable pins.

The additional pin may be resiliently biased relative to the moveablepins.

The partition may be connected to or may form part of a supportstructure.

Ends of the manipulators may be provided with a coating of robustmaterial.

The pellicle frame attachment apparatus may include a gas outlet in thecontrolled environment, the gas outlet being configured to supply gas ata pressure which is higher than a gas pressure on an opposite side ofthe partition.

According to a third aspect of the invention there is provided a studattachment apparatus comprising a support structure configured to hold apatterning device and a stud manipulator configured to bring a stud intocontact with the patterning device, wherein the stud manipulator isseparated from a patterning device receiving controlled environment by apartition, the partition including a hole through which the stud mayproject in order to contact the patterning device.

The stud manipulator may be one of a plurality of stud manipulators, andthe hole in the partition may be one of a plurality of holes.

The stud attachment apparatus may include a gas outlet in the controlledenvironment, the gas outlet being configured to supply gas at a pressurewhich is higher than a gas pressure on an opposite side of thepartition.

A seal may be provided around the stud manipulator. The seal may, inuse, provide a seal relative to the patterning device to isolate a studreceiving part of the patterning device from other parts of thepatterning device.

At least one gas delivery channel and at least one gas extractionchannel may be provided via which a flow of gas may be provided to andfrom the stud receiving part of the patterning device.

The seal may be a leakage seal.

The stud manipulator may include a heater.

The partition may include windows positioned to allow alignment marks onthe patterning device to be visible from an opposite side of thepartition.

Imaging sensors may be provided on one side of the windows and areconfigured to look through the windows to view the alignment marks onthe patterning device.

A kinematic connection may be provided between the stud manipulator andthe support structure.

According to a fourth aspect of the invention there is provided a studremoval apparatus comprising a support structure configured to hold apatterning device, a stud gripper which is configured to receive andretain a distal head of a stud projecting from the patterning device,actuators configured to move the stud gripper relative to the stud andpatterning device, and a heater.

The stud gripper may comprise a pair of flanges with a separation whichis wider than a neck of the stud and narrower than a distal head of thestud.

The stud removal apparatus may further comprise a weight which isconnected to the stud gripper and pulls downwardly on the stud gripper.

The stud removal apparatus may further comprise a pusher arm which ismoveable in a generally horizontal direction relative to the studgripper, the pusher arm being configured to push a stud out of the studgripper after it has been removed from a patterning device.

The stud removal apparatus may further comprise a chute which isconfigured to guide studs which have been pushed out of the studgripper.

The stud removal apparatus may further comprise a stud receptaclelocated at an outlet of the chute.

According to a fifth aspect of the invention there is provided alithographic system comprising a pellicle frame attachment apparatusconfigured to receive a patterning device, a pellicle frame and apellicle and attach the pellicle frame to the patterning device so as toform a mask assembly in which the pellicle frame supports the pellicleadjacent the patterning device, a lithographic apparatus comprising asupport structure configured to receive the mask assembly from thepellicle frame attachment apparatus and support the mask assembly, anillumination system configured to condition a radiation beam andilluminate the mask assembly with the conditioned radiation beam, thepatterning device of the mask assembly being configured to impart theconditioned radiation beam with a pattern in its cross-section to form apatterned radiation beam, a substrate table constructed to hold asubstrate and a projection system configured to project the patternedradiation beam onto the substrate, the lithographic system furthercomprising a mask assembly transport device configured to transport themask assembly from the pellicle frame attachment apparatus to thelithographic apparatus for use in the lithographic apparatus.

The pellicle frame attachment apparatus may be configured to attach thepellicle frame to the patterning device in a sealed environment.

The pellicle frame attachment apparatus may comprise a vacuum pumpconfigured to pump the sealed environment of the pellicle frameattachment apparatus to vacuum pressure conditions.

The mask assembly transport device may be configured to transport themask assembly from the pellicle frame attachment apparatus to thelithographic apparatus in a sealed environment.

The mask assembly transport device may comprise a vacuum pump configuredto pump the sealed environment of the mask assembly attachment apparatusto vacuum pressure conditions.

The lithographic system may further comprise an inspection apparatusconfigured to inspect one or more of the pellicle, pellicle frame andpatterning device for at least one of contamination or defects.

The pellicle frame attachment apparatus may be configured to receive apellicle attached to a pellicle frame and attach the pellicle frame withthe pellicle attached to a patterning device.

The illumination system may be configured to condition an EUV radiationbeam.

The pellicle frame attachment apparatus may be configured to receive apellicle which is substantially transparent to EUV radiation.

According to a sixth aspect of the invention there is provided apellicle attachment apparatus configured to receive a pellicle and apellicle frame, attach the pellicle to the pellicle frame to form apellicle assembly and seal the pellicle assembly in a sealed packagingsuitable for transportation of the pellicle assembly within the sealedpackaging.

The pellicle attachment apparatus may be configured to attach thepellicle to the pellicle frame in a sealed environment.

The pellicle attachment apparatus may further comprise a vacuum pumpconfigured to pump the sealed environment to vacuum pressure conditions.

The pellicle attachment apparatus may further comprise an inspectionapparatus configured to inspect one or both of the pellicle and pellicleframe for at least one of contamination or defects.

According to a seventh aspect of the invention there is provided amethod of attaching a pellicle to a pellicle frame, the methodcomprising using a pellicle frame handling system to place the pellicleframe on a support structure, applying glue to the pellicle frame,holding a pellicle above the pellicle frame using a pellicle handlingsystem, aligning the pellicle frame and the pellicle, and placing thepellicle onto the pellicle frame.

Alignment of the pellicle frame and the pellicle may be achieved bymoving the support structure which supports the pellicle frame.

The method may further comprise pressing downwardly onto the pellicleusing arms, thereby holding the pellicle on the pellicle frame duringcuring of the glue.

The glue may be provided at spaced apart locations. An arm may pressdown onto the pellicle at each spaced apart location.

According to an eighth aspect of the invention there is provided amethod of attaching a pellicle assembly to a patterning device, thepellicle assembly comprising a pellicle frame and a pellicle, the methodcomprising placing the pellicle assembly on a first part of the supportstructure, placing the patterning device on a second part of the supportstructure, with studs of the patterning device facing towards thepellicle assembly, lifting the pellicle assembly from the supportstructure then moving the pellicle assembly to align it relative to thepatterning device, and using manipulators to operate engagementmechanisms of sub-mounts provided on the pellicle frame, themanipulators engaging the engagement mechanisms with the studsprojecting from the patterning device.

The manipulators may comprise hooked arms and manipulator pins which areused to move engagement arms of each engagement mechanism relative tosupport arms of each engagement mechanism in order to create space toreceive a distal head of one of the studs.

The hooked arms may hold the support arm of the engagement mechanismwhile the manipulator pins push engagement arms of the engagementmechanism upwards.

Lifting of the pellicle assembly may be performed using additional pins

According to a ninth aspect of the invention there is provided a methodof attaching studs to a patterning device, the method comprising placingthe studs in stud manipulators provided on a support structure, applyingglue to the studs, placing the patterning device above the studs andwith a patterned surface facing downwards, and moving the studmanipulators upwards to move the studs into contact with the patterningdevice.

The method may further comprise heating the studs using heaters in thestud manipulators in order to cure the glue.

A seal may be provided around each stud manipulator and wherein gas isdelivered to the stud manipulator and then removed from the studmanipulator in order to carry contamination away from the vicinity ofthe seal.

The seal may be a leakage seal

According to a tenth aspect of the invention there is provided a methodof removing a stud from a patterning device, the method comprisingsupporting the patterning device using a support, with the patterningdevice being oriented such that the stud projects downwardly from thepatterning device, moving a stud gripper relative to the stud andthereby receiving and retaining a distal head of the stud, heating thestud gripper and thereby heating the stud to melt glue located betweenthe stud and the patterning device, and pulling the stud downwards usingthe stud gripper such that the stud separates from the patterning devicewhen the glue melts.

The stud may be pulled downwards by a weight which is connected to thestud gripper and pulls downwardly on the stud gripper.

The method may further comprise using a pusher arm to push the stud outof the stud gripper after it has been removed from a patterning device.

The method may further comprise using a chute to direct the stud to astud receptacle.

It will be appreciated that one or more aspects or features describedabove or referred to in the following description may be combined withone or more other aspects or features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings, in which:

FIG. 1 is a schematic illustration of a lithographic system comprising alithographic apparatus and a radiation source;

FIG. 2 is a schematic illustration of various apparatuses and alithographic apparatus according to embodiments of the invention;

FIG. 3 is a perspective view a mask assembly according to an embodimentof the invention;

FIG. 4 is a cross sectional view of part of the mask assembly of FIG. 3;

FIGS. 5A-5B depicts an engagement mechanism which forms part of the maskassembly of FIG. 3;

FIG. 6 schematically depicts a pellicle attachment apparatus accordingto an embodiment of the invention;

FIG. 7 depicts parts of the pellicle attachment apparatus in moredetail;

FIG. 8 depicts in perspective view a handling system according to anembodiment of the invention;

FIG. 9 depicts part of the handling system of FIG. 8 in more detail;

FIG. 10 schematically depicts part of the pellicle attachment apparatusviewed from above;

FIG. 11 depicts an arm of the pellicle attachment apparatus incross-section;

FIG. 12 schematically depicts a pellicle frame attachment apparatusaccording to an embodiment of the invention;

FIG. 13 is a perspective view of part of the pellicle frame attachmentapparatus;

FIG. 14 shows part of pellicle frame attachment apparatus in greaterdetail;

FIG. 15 schematically depicts an interrelationship between differentparts of the pellicle frame attachment apparatus;

FIGS. 16 and 17 schematically depict operation of an engagementmechanism by the pellicle frame attachment apparatus;

FIGS. 18A-18H depict in more detail operation of the engagementmechanism by the pellicle frame attachment apparatus;

FIG. 19 schematically depicts a stud attachment apparatus according toan embodiment of the invention;

FIG. 20 is a perspective view of the stud attachment apparatus;

FIG. 21 depicts in cross-section part of the stud attachment apparatus;

FIG. 22 depicts part of the stud attachment apparatus viewed from above;

FIG. 23 depicts the stud attachment apparatus viewed from above but witha partition having been removed;

FIG. 24 depicts part of the stud attachment apparatus in a partiallydisassembled state;

FIG. 25 is a perspective view of a stud remover which forms part of astud removal apparatus according to an embodiment of the invention;

FIG. 26 is a perspective view of part of the stud remover in moredetail; and

FIGS. 27 to 29 are cross-sectional views of part of the stud remover.

DETAILED DESCRIPTION

FIG. 1 shows a lithographic system including a mask assembly accordingto one embodiment of the invention. The lithographic system comprises aradiation source SO and a lithographic apparatus LA. The radiationsource SO is configured to generate an extreme ultraviolet (EUV)radiation beam B. The lithographic apparatus LA comprises anillumination system IL, a support structure MT configured to support amask assembly 15 including a patterning device MA (e.g., a mask), aprojection system PS and a substrate table WT configured to support asubstrate W. The illumination system IL is configured to condition theradiation beam B before it is incident upon the patterning device MA.The projection system is configured to project the radiation beam B (nowpatterned by the patterning device MA) onto the substrate W. Thesubstrate W may include previously formed patterns. Where this is thecase, the lithographic apparatus aligns the patterned radiation beam Bwith a pattern previously formed on the substrate W.

The radiation source SO, illumination system IL, and projection systemPS may all be constructed and arranged such that they can be isolatedfrom the external environment. A gas at a pressure below atmosphericpressure (e.g., hydrogen) may be provided in the radiation source SO. Avacuum may be provided in the illumination system IL and/or theprojection system PS. A small amount of gas (e.g., hydrogen) at apressure well below atmospheric pressure may be provided in theillumination system IL and/or the projection system PS.

The radiation source SO shown in FIG. 1 is of a type that may bereferred to as a laser produced plasma (LPP) source. A laser 1, whichmay for example be a CO2 laser, is arranged to deposit energy via alaser beam 2 into a fuel, such as tin (Sn) that is provided from a fuelemitter 3. Although tin is referred to in the following description, anysuitable fuel may be used. The fuel may for example be in liquid form,and may for example be a metal or alloy. The fuel emitter 3 may comprisea nozzle configured to direct tin, e.g., in the form of droplets, alonga trajectory towards a plasma formation region 4. The laser beam 2 isincident upon the tin at the plasma formation region 4. The depositionof laser energy into the tin creates a plasma 7 at the plasma formationregion 4. Radiation, including EUV radiation, is emitted from the plasma7 during de-excitation and recombination of ions of the plasma.

The EUV radiation is collected and focused by a near normal incidenceradiation collector 5 (sometimes referred to more generally as a normalincidence radiation collector). The collector 5 may have a multilayerstructure that is arranged to reflect EUV radiation (e.g., EUV radiationhaving a desired wavelength such as 13.5 nm). The collector 5 may havean elliptical configuration, having two ellipse focal points. A firstfocal point may be at the plasma formation region 4, and a second focalpoint may be at an intermediate focus 6, as discussed below.

In other embodiments of a laser produced plasma (LPP) source thecollector 5 may be a so-called grazing incidence collector that isconfigured to receive EUV radiation at grazing incidence angles andfocus the EUV radiation at an intermediate focus. A grazing incidencecollector may, for example, be a nested collector, comprising aplurality of grazing incidence reflectors. The grazing incidencereflectors may be disposed axially symmetrically around an optical axisO.

The radiation source SO may include one or more contamination traps (notshown).

For example, a contamination trap may be located between the plasmaformation region 4 and the radiation collector 5. The contamination trapmay for example be a rotating foil trap, or may be any other suitableform of contamination trap.

The laser 1 may be separated from the radiation source SO. Where this isthe case, the laser beam 2 may be passed from the laser 1 to theradiation source SO with the aid of a beam delivery system (not shown)comprising, for example, suitable directing mirrors and/or a beamexpander, and/or other optics. The laser 1 and the radiation source SOmay together be considered to be a radiation system.

Radiation that is reflected by the collector 5 forms a radiation beam B.The radiation beam B is focused at point 6 to form an image of theplasma formation region 4, which acts as a virtual radiation source forthe illumination system IL. The point 6 at which the radiation beam B isfocused may be referred to as the intermediate focus. The radiationsource SO is arranged such that the intermediate focus 6 is located ator near to an opening 8 in an enclosing structure 9 of the radiationsource.

The radiation beam B passes from the radiation source SO into theillumination system IL, which is configured to condition the radiationbeam. The illumination system IL may include a facetted field mirrordevice 10 and a facetted pupil mirror device 11. The faceted fieldmirror device 10 and faceted pupil mirror device 11 together provide theradiation beam B with a desired cross-sectional shape and a desiredangular distribution. The radiation beam B passes from the illuminationsystem IL and is incident upon the mask assembly 15 held by the supportstructure MT. The mask assembly 15 includes a patterning device MA and apellicle 19, which is held in place by a pellicle frame 17. Thepatterning device MA reflects and patterns the radiation beam B. Theillumination system IL may include other mirrors or devices in additionto or instead of the faceted field mirror device 10 and faceted pupilmirror device 11.

Following reflection from the patterning device MA the patternedradiation beam B enters the projection system PS. The projection systemcomprises a plurality of mirrors that are configured to project theradiation beam B onto a substrate W held by the substrate table WT. Theprojection system PS may apply a reduction factor to the radiation beam,forming an image with features that are smaller than correspondingfeatures on the patterning device MA. A reduction factor of 4 may forexample be applied. Although the projection system PS has two mirrors inFIG. 1, the projection system may include any number of mirrors (e.g.,six mirrors).

The lithographic apparatus may, for example, be used in a scan mode,wherein the support structure (e.g., mask table) MT and the substratetable WT are scanned synchronously while a pattern imparted to theradiation beam is projected onto a substrate W (i.e., a dynamicexposure). The velocity and direction of the substrate table WT relativeto the support structure (e.g., mask table) MT may be determined by thedemagnification and image reversal characteristics of the projectionsystem PS. The patterned radiation beam that is incident upon thesubstrate W may comprise a band of radiation. The band of radiation maybe referred to as an exposure slit. During a scanning exposure, themovement of the substrate table WT and the support structure MT may besuch that the exposure slit travels over an exposure field of thesubstrate W.

The radiation source SO and/or the lithographic apparatus that is shownin FIG. 1 may include components that are not illustrated. For example,a spectral filter may be provided in the radiation source SO. Thespectral filter may be substantially transmissive for EUV radiation butsubstantially blocking for other wavelengths of radiation such asinfrared radiation.

In other embodiments of a lithographic system the radiation source SOmay take other forms. For example, in alternative embodiments theradiation source SO may comprise one or more free electron lasers. Theone or more free electron lasers may be configured to emit EUV radiationthat may be provided to one or more lithographic apparatus.

As was described briefly above, the mask assembly 15 includes a pellicle19 that is provided adjacent to the patterning device MA. The pellicle19 is provided in the path of the radiation beam B such that radiationbeam B passes through the pellicle 19 both as it approaches thepatterning device MA from the illumination system IL and as it isreflected by the patterning device MA towards the projection system PS.The pellicle 19 comprises a thin film that is substantially transparentto EUV radiation (although it will absorb a small amount of EUVradiation). By EUV transparent pellicle or a film substantiallytransparent for EUV radiation herein is meant that the pellicle 19 istransmissive for at least 65% of the EUV radiation, preferably at least80% and more preferably at least 90% of the EUV radiation. The pellicle19 acts to protect the patterning device MA from particle contamination.

Whilst efforts may be made to maintain a clean environment inside thelithographic apparatus LA, particles may still be present inside thelithographic apparatus LA. In the absence of a pellicle 19, particlesmay be deposited onto the patterning device MA. Particles on thepatterning device MA may disadvantageously affect the pattern that isimparted to the radiation beam B and the pattern that is transferred tothe substrate W. The pellicle 19 advantageously provides a barrierbetween the patterning device MA and the environment in the lithographicapparatus LA in order to prevent particles from being deposited on thepatterning device MA.

The pellicle 19 is positioned at a distance from the patterning deviceMA that is sufficient that any particles that are incident upon thesurface of the pellicle 19 are not in the focal plane of the radiationbeam B. This separation between the pellicle 19 and the patterningdevice MA acts to reduce the extent to which any particles on thesurface of the pellicle 19 impart a pattern to the radiation beam B. Itwill be appreciated that where a particle is present in the beam ofradiation B, but at a position that is not in a focal plane of the beamof radiation B (i.e., not at the surface of the patterning device MA),then any image of the particle will not be in focus at the surface ofthe substrate W. In the absence of other considerations it may bedesirable to position the pellicle 19 a considerable distance away fromthe patterning device MA. However, in practice the space which isavailable in the lithographic apparatus LA to accommodate the pellicleis limited due to the presence of other components. In some embodiments,the separation between the pellicle 19 and the patterning device MA may,for example, be approximately between 1 mm and 10 mm, for examplebetween 1 mm and 5 mm, more preferably between 2 mm and 2.5 mm.

A mask assembly may be prepared for use in a lithographic apparatus byattaching a pellicle to a pellicle frame and by attaching the pellicleframe to a patterning device. A mask assembly comprising a patterningdevice MA and a pellicle supported adjacent to the patterning device bya pellicle frame may be prepared remotely from a lithographic apparatusLA and the mask assembly may be transported to the lithographicapparatus LA for use in the lithographic apparatus LA. For example, apellicle frame supporting a pellicle may be attached to a patterningdevice, so as to form a mask assembly, at a site at which a pattern isimparted onto the patterning device. The mask assembly may then betransported to a separate site at which a lithographic apparatus LA issituated and the mask assembly may be provided to the lithographicapparatus LA for use in the lithographic apparatus LA.

A mask assembly in which a pellicle is held in place by a pellicle framemay be delicate and transport of the mask assembly may risk damage tothe pellicle. Assembling a mask assembly in a separate environment to alithographic apparatus LA may additionally result in the mask assemblybeing exposed to a variety of pressure conditions. For example, a maskassembly may be transported to a lithographic apparatus under ambientpressure conditions. The mask assembly may then be loaded into thelithographic apparatus LA via a load lock which is pumped to vacuumpressure conditions. Changes in the pressure conditions to which a maskassembly is exposed may cause a pressure difference to exist across apellicle which may cause the pellicle to bend and may risk damage to thepellicle. In an embodiment, a lithographic system may comprise alithographic apparatus LA connected to a pellicle frame attachmentapparatus. Where this is the case a mask assembly comprising a mask andpellicle may be transferred directly from the pellicle frame attachmentapparatus to the lithographic apparatus whilst remaining in a controlledenvironment (e.g. a vacuum environment).

FIG. 2 is a schematic illustration of apparatus suitable for assemblinga mask assembly 15 and transferring the mask assembly to a lithographicapparatus LA. FIG. 2 depicts a pellicle attachment apparatus 855 whichmay be used to attach a pellicle 19 to a pellicle frame 17, and apellicle assembly transport device 881 which may be used to transportthe pellicle assembly. In addition a stud attachment apparatus 840 isdepicted, which may be used to attach studs 51 to a patterning deviceMA. The studs 51 allow releasable attachment of the pellicle frame 17(and pellicle 19) to the patterning device MA. A mask transport device880 which may be used to transport the mask with attached studs is alsodepicted. A pellicle frame attachment apparatus 857 which may be used toattach a pellicle frame 17 (and pellicle 19) to a patterning device MA,thereby forming a mask assembly 15, is also depicted. A mask assemblytransport device 853 which may be used to transport the mask assembly 15from the pellicle frame attachment apparatus 857 to the lithographicapparatus LA is also shown.

The pellicle attachment apparatus 855 may be situated at a differentsite from the site at which the lithographic apparatus is situated. Thestud attachment apparatus 840 may be situated at a different site fromthe site at which the lithographic apparatus LA is situated.Alternatively, either or both of the pellicle attachment apparatus 855and the stud attachment apparatus 840 may be located at the same site asthe site at which the lithographic apparatus LA is situated (e.g. in alithographic fab).

The pellicle attachment apparatus 855 receives a pellicle 19, a pellicleframe 17 and engagement mechanisms (not illustrated). The pellicle 19and pellicle frame 17 may be manually placed in the pellicle attachmentapparatus 855. Glue is dispensed at engagement mechanism receivingopenings in the pellicle frame 17 (e.g. locations described furtherbelow). Glue dispensing may be manual, or may be automated (or partiallyautomated). The engagement mechanisms and the pellicle frame 17 arealigned relative to each other (e.g. using an optical alignmentapparatus), and the engagement mechanisms are then inserted into theopenings in the pellicle frame.

Glue is also dispensed onto the pellicle frame 17 (e.g. at spaced apartlocations around the pellicle frame 17). Glue dispensing may be manual,or may be automated (or partially automated). An optical alignmentsystem is used to align the pellicle 19 relative to the pellicle frame17, and the pellicle is then pressed against the pellicle frame.

The pellicle 19 is held pressed against the pellicle frame 17 at roomtemperature for a period of time sufficient to allow the glue to cure,thereby securing the pellicle to the pellicle frame. The pressure on thepellicle 19 is then removed. Additional curing of the glue at anelevated temperature is then performed using a curing oven (which mayform part of the pellicle attachment apparatus). This will also cureglue which attaches the engagement mechanisms to the pellicle frame 17.In an alternative approach, some heating may be applied to cure the gluewhen the pellicle 19 is being held against the pellicle frame (insteadof allowing curing to proceed at room temperature).

Although the use of glue to attach the pellicle 19 to the pellicle frame17 is described above, the pellicle may be attached to the pellicleframe using any suitable type of bonding (including without using glue).

The resulting pellicle assembly 16 is inspected using a particleinspection tool. The particle inspection tool may form part of thepellicle attachment apparatus 855 (or may be a separate tool). Theparticle inspection tool may be configured to inspect for particlesdisposed on the pellicle 19 and/or the pellicle frame 17. The particleinspection tool may, for example, reject a pellicle assembly which has anumber of particles which is greater than a given particle threshold.The particle inspection tool may also be used to inspect a pellicle 19and/or a pellicle frame 17 before the pellicle and pellicle frame areglued together.

The pellicle attachment apparatus 855 may be configured, followinginspection, to seal the pellicle assembly 16 in a pellicle assemblytransport device 881 (a sealed box). As depicted, the pellicle assemblytransport device 881 may be arranged to hold the pellicle assembly in anorientation in which the pellicle 19 is below the pellicle frame 17.Because the transport device 881 is sealed, the pellicle assembly can betransported without the pellicle assembly 16 being contaminated. Thepellicle assembly 16 may be transported in the transport device 881 to apellicle frame attachment apparatus 857.

The pellicle attachment apparatus 855 may include a clean environment soas to reduce the number of particles inside the sealed environment,thereby reducing the number or particles which may be deposited on thepellicle 19. The pellicle attachment apparatus 855 may, for example, besituated at a site at which pellicles are manufactured. In someembodiments a pellicle 19 may be provided to the pellicle attachmentapparatus 855 directly from a pellicle manufacturing tool (not shown) inwhich the pellicle 19 is manufactured. A pellicle 19 may, for example,be provided to the pellicle attachment apparatus 855 from a pelliclemanufacturing tool whilst keeping the pellicle 19 inside a cleanenvironment. This may reduce the chance of a pellicle 19 from beingcontaminated or damaged before being provided to the pellicle attachmentapparatus 855. The clean environment may, for example be a sealedenvironment (i.e. fully isolated from an external environment). Thesealed environment may be pumped so as to maintain a vacuum in thesealed environment.

The attachment of the pellicle 19 to the pellicle frame 17 may becontrolled so as to achieve a desirable tension in the pellicle 19. Forexample, the tension in the pellicle 19 may be measured during or afterattachment of the pellicle 19 to the pellicle frame 17 and the tensionmay be adjusted in response to the measurement in order to achieve adesirable tension in the pellicle 19. The tension in the pellicle 19 maybe maintained, for example, by applying an outward force to componentsof the pellicle frame 17 so as to stretch the pellicle 19. Tension inthe pellicle 19 may for example be maintained by using differences inthermal expansion coefficients between the pellicle frame and thepellicle.

In an embodiment, the patterning device (which may be referred to as amask) MA may be provided with protrusions which are received byengagement mechanisms (e.g. as described further below). The patterningdevice may for instance receive four protrusions (referred to herein asstuds). As depicted in FIG. 2, the stud attachment apparatus 840 may beused to attach studs 51 to the patterning device MA.

The studs 51 and the patterning device MA may be manually placed in thestud attachment apparatus 840. The patterning device MA may be held in acontrolled environment 841 which is separated from the rest of the studattachment apparatus 840. Separation may be provided by a partition 842with openings through which the studs 51 may project in order to contactthe patterning device MA. The controlled environment 841 may be held ata higher pressure than other parts of the stud attachment apparatus 840(e.g. by delivering gas through an outlet in the controlledenvironment). This will inhibit or prevent passage of contaminationparticles into the controlled environment 841 from other parts of thestud attachment apparatus.

The stud attachment apparatus 840 may include a stud manipulator (notdepicted), such as a robot or actuators for accurately placing thestuds. An example of a suitable actuator for placing studs onto thepatterning device is a Lorentz actuator (not depicted). The studattachment apparatus 840 may also include a device for automaticallyproviding a given amount of glue or adhesive to the stud surface to beattached to the patterning device MA (although applying a glue oradhesive may also be done manually in advance). Contamination of themask MA by contaminants from the glue or adhesive is prevented orreduced by a flow of air from the controlled environment above thepartition 842 to below the partition (the flow of air is caused by thepressure above the partition being higher than the pressure below thepartition).

The stud attachment apparatus 840 may further include an opticalalignment system which aligns the studs with respect to the alignmentmarkers present on the reticle in order to accurately position thestuds. For example, the alignment markers conventionally provided on thepatterning device MA and used for pattern alignment may also be used foraligning the studs.

The stud attachment apparatus may include a support structure movable inthe X-Y-Z and Rz directions for adjusting the position of the patterningdevice MA. The position of the support structure holding the patterningdevice MA may be adjustable manually by means of coarse and finemechanical adjusting devices, or using automated (or semi-automated)actuators or any other type of devices suitable for alignment andpositioning which are coupled to the patterning device table.

Once the studs 51 and the patterning device MA have been aligned, thestuds are then pressed against the patterning device MA. The studs 51may be held against the patterning device MA at room temperature for aperiod of time which is sufficient to allow the glue to cure, therebysecuring the studs to the mask. Alternatively, the studs 51 may beheated in order to accelerate curing of the glue. Additional curing ofthe glue at an elevated temperature may then be performed using a curingoven (which may form part of the stud attachment apparatus 840).

The patterning device MA and studs 51 may be inspected using a particleinspection tool (which may form part of the stud attachment apparatus840).

The stud attachment apparatus 840 seals the patterning device MA andstuds 51 in a patterning device MA transport device 880 (a sealed box).Because the mask transport device 880 is sealed, the patterning deviceMA and studs 51 can be transported without the mask being contaminated.The patterning device MA and studs may be transported in the transportdevice 880 to the pellicle frame attachment apparatus 857.

In an embodiment, the mask is provided to the stud attachment apparatus840 in a sealed box (to reduce the risk of contamination). The box mayremain sealed until just before the studs 51 are to be attached to thepatterning device MA, thereby minimizing the time during whichcontamination could travel to the mask.

The controlled environment 841 of the stud attachment apparatus 840 maybe provided in part by a housing which subsequently forms part of thepatterning device MA transport device 880 (a sealed box). The housingmay form walls and a roof of the transport device 880, with a floor ofthe transport device being formed by a plate that is fitted after thestuds 51 have been attached (e.g. immediately afterwards). Using thehousing in this way may assist in preventing contamination from beingincident upon the patterning device MA. The housing may comprise a coverof a pod. The mask table of the stud attachment apparatus 840 may beconfigured to receive the housing.

Similarly, the pellicle attachment apparatus 855 may also be formed inpart by a housing that subsequently forms part of the pellicle assemblytransport device 881.

The pellicle assembly 16 in the transport device 881 and the patterningdevice MA (and studs 51) in the transport device 880 are bothtransported to the pellicle frame attachment apparatus 857. The pellicleframe attachment apparatus 857 may be provided in a fab in which one ormore lithographic apparatus are also provided.

The pellicle frame attachment apparatus 857 is configured to attach thepellicle frame 17 of the pellicle assembly 16 to the studs 51 on thepatterning device MA so as to form a mask assembly 15. The pellicleframe attachment apparatus 857 may include a controlled environment 860which is separated from the rest of the pellicle frame attachmentapparatus. Separation may be provided by a partition 862 with openingsthrough which manipulators extend (not shown in FIG. 2). Themanipulators may be operated by a control system 870 (described furtherbelow). The controlled environment 860 may be maintained as a cleanenvironment so as to reduce the number of particles inside thecontrolled environment, thereby reducing the number of particles whichmay be deposited on the mask assembly 15. The controlled environment 860may be held at a higher pressure than other parts of the pellicle frameattachment apparatus 857 (e.g. by delivering gas through an outlet inthe controlled environment). This will inhibit or prevent passage ofcontamination particles into the controlled environment 860 from otherparts of the pellicle frame attachment apparatus 857.

The mask assembly 15 which is assembled by the pellicle frame attachmentapparatus 857 is transported from the pellicle frame attachmentapparatus to the lithographic apparatus LA in a mask assembly transportdevice 853. The mask assembly transport device 853 may comprise a sealedand clean environment in which the mask assembly 15 is transported. Thisreduces the chances of the mask assembly 15 being contaminated ordamaged during transport of the mask assembly. The sealed and cleanenvironment may, for example, be pumped to a vacuum.

The pellicle frame attachment apparatus 857 may be used to mount,demount or remount the pellicle assembly 16 to/from the patterningdevice. The pellicle frame attachment apparatus 857 may comprisemanipulators arranged to manipulate engagement mechanisms of thepellicle frame (as described further below).

The patterning device MA may, for example, be provided with alignmentmarks. The pellicle frame 17 may be positioned relative to the alignmentmarks on the patterning device. Aligning the pellicle frame 17 relativeto alignment marks on the patterning device may advantageously increasethe accuracy with which the pellicle frame 17 is positioned on thepatterning device MA during attachment of the pellicle frame 17 to thepatterning device MA.

In some embodiments the patterning device MA may be cleaned in thepellicle frame attachment apparatus 857, for example, to removeparticles from the patterning device MA. In other embodiments cleaningof the patterning device MA may be performed in a dedicated cleaningtool.

Although illustrated embodiments show the pellicle frame being attachedat the front of the mask, in other embodiments the pellicle frame may beattached at other parts of the mask. For example, the pellicle frame maybe attached to sides of the mask. This may be achieved for example usingsub-mounts which provide releasably engageable attachment between thepellicle frame and sides of the mask. In an alternative arrangement thepellicle frame may be attached to the mask through a combination of someattachment locations on sides of the mask and some attachment locationson the front of the mask. Attachment may for example be provided bysub-mounts which releasably engage the pellicle frame and the mask.

In some embodiments the pellicle frame attachment apparatus 857 mayinclude a particle inspection tool (not shown). The particle inspectiontool may be configured to inspect the mask assembly 15 for particlesdisposed on the mask assembly 15. The particle inspection tool may, forexample, reject mask assemblies 15 which have a number of particlesdisposed on them which is greater than a given particle threshold.

In some embodiments the pellicle frame attachment apparatus 857 mayinclude a pattern inspection system which inspects the pattern on thepatterning device for any defects. The pattern inspection system mayinspect the pattern on the patterning device before and/or after thepellicle frame 17 is attached to the patterning device MA.

The attachment of the pellicle frame 17 to the patterning device MA maybe controlled so as to achieve a desirable tension in the pellicle 19.For example, the tension in the pellicle 19 may be measured duringattachment of the pellicle frame 17 to the patterning device MA and thetension may be adjusted in response to the measurement in order toachieve a desired tension in the pellicle 19.

The lithographic apparatus LA may, for example, correspond with thelithographic apparatus LA which is depicted in FIG. 1. The lithographicapparatus LA may include components which are configured to receive amask assembly 15 from the mask assembly transport device 853 and loadthe mask assembly 15 onto a support structure MT of the lithographicapparatus LA. The mask assembly 15 may be illuminated with a conditionedradiation beam B provided by an illumination system IL. The patterningdevice MA of the mask assembly 15 may impart the conditioned radiationbeam with a pattern in its cross-section to form a patterned radiationbeam. The patterned radiation beam may be projected by a projectionsystem PS onto a substrate W held by a substrate table WT. Theconditioned radiation beam may, for example, comprise EUV radiation. Inembodiments in which the conditioned radiation beam comprises EUVradiation the pellicle 19 of the mask assembly 15 may be substantiallytransparent to EUV radiation.

In some embodiments a pellicle assembly 16 may be attached to apatterning device MA so as to form a mask assembly 15 under vacuumconditions in the pellicle frame attachment apparatus 857. The maskassembly 15 may subsequently be transported to the lithographicapparatus LA under vacuum conditions by the mask assembly transportdevice 853 and may be held under vacuum conditions in the lithographicapparatus LA. The mask assembly 15 may therefore be exposed toapproximately the same pressure conditions throughout its assembly inthe pellicle frame attachment apparatus 857 and use in the lithographicapparatus LA. This advantageously reduces any pressure changes to whichthe mask assembly 15 is exposed and therefore reduces any pressuredifferences which may develop across the pellicle 19.

In some embodiments the patterning device MA and/or the pellicle 19 maybe inspected for particles and/or defects in the pellicle frameattachment apparatus 857 whilst the components are held in a vacuum. Thepatterning device MA and/or the pellicle 19 are therefore advantageouslyinspected under similar pressure conditions to those to which they areexposed during use in the lithographic apparatus LA. This isadvantageous since any particles which may be deposited onto patterningdevice MA and/or the pellicle during pumping down to vacuum conditionsmay be detected in the pellicle frame attachment apparatus 857.

In some embodiments the lithographic system LS may further comprise aseparate inspection apparatus (not shown) which is configured to inspectone or more components of a mask assembly 15 for particles and/ordefects. A mask assembly 15 may, for example, be transported to aninspection apparatus (e.g. by the mask assembly transport device 853)after being assembled in the pellicle frame attachment apparatus 857 andprior to transporting the mask assembly 15 to the lithographic apparatusLA.

Embodiments of the invention as described above advantageously allow amask assembly 15 to be assembled and passed to a lithographic apparatusLA in an automated (or semi-automated) process. The assembly andtransport of the mask assembly 15 may all be conducted in a sealed cleanenvironment which may, for example, be pumped to vacuum pressureconditions. This may reduce the chance of components of the maskassembly 15 from being contaminated or damaged prior to the use of themask assembly 15 in a lithographic apparatus LA.

In general, the useful lifetime of a pellicle 19 may be less than theuseful lifetime of a patterning device MA. It may therefore be desirableto remove a pellicle assembly 16 from patterning device MA and replacethe pellicle assembly with a new pellicle assembly so as to allow forcontinued use of the patterning device MA. Replacement of a pellicleassembly 16 may, for example, be carried out in the pellicle frameattachment apparatus 857. For example, after use in the lithographicapparatus LA, a mask assembly 15 may be passed back to the pellicleframe attachment apparatus 857 using the mask assembly transport device853 for pellicle assembly replacement in the pellicle frame attachmentapparatus 857. The patterning device MA may be subjected to a cleaningprocess so as to remove contamination from the patterning device MAafter the pellicle assembly 16 has been removed. The studs 51 may beremoved from the patterning device MA before the patterning device issubjected to the cleaning process.

It will be noted that the patterned side of the patterning device MA isdirected downwards during the various operations that are depicted inFIG. 2. Keeping the patterned side of the patterning device MA facingdownwards is advantageous because this reduces the likelihood of acontamination particle being incident upon the pattern. Largercontamination particles tend to fall downwards due to gravity and thuswill be incident upon the opposite side of the mask. Smallercontamination particles are less influenced by gravity and may insteadbe influenced by other transport physics. Apparatus of embodiments ofthe invention may include devices intended to address this. For example,the apparatus may include an ionizer to remove static charges andthereby reduce the risk of electrostatics causing particles to becomeattached to the pellicle.

A mask assembly according to an embodiment of the invention isillustrated in FIGS. 3-5. In this embodiment a pellicle frame andpellicle are suspended relative to a patterning device (e.g. a mask).The pellicle frame is releasably engageable with the patterning device.The releasable engagement is provided by a mount which comprises aplurality of sub-mounts (for example 2, 3, 4 or even more sub-mounts).The mount allows the pellicle frame (and pellicle) to be removed fromthe patterning device in an easy and convenient manner. The removal ofthe pellicle frame and pellicle from the patterning device may be clean,i.e. may generate substantially no contamination particles. Once thepellicle frame has been removed from the patterning device thepatterning device may be inspected using an inspection tool (and may becleaned if necessary). The pellicle frame and pellicle can subsequentlybe easily reattached to the patterning device or may be replaced with anew pellicle frame and pellicle.

Referring first to FIG. 3, a pellicle 19 is attached to a pellicle frame17. The pellicle 19 may, for example, be glued to the pellicle frame 17.The pellicle frame 17 is provided with four engagement mechanisms 50A-D.Each engagement mechanism 50A-D is configured to receive a protrusion(which may for example be referred to as a stud) which extends from apatterning device (as described below in connection with FIG. 4). Twoengagement mechanisms 50A,B are provided on one side of the pellicleframe 17 and two engagement mechanisms 50C,D are provided on an oppositeside of the pellicle frame. Other combinations may also be possible,such as an engagement mechanism on each of the four frame sides etc. Theengagement mechanisms are provided on sides of the pellicle frame 17which will be oriented in the scanning direction during use in alithographic apparatus (indicated in FIG. 3 as the y-direction inaccordance with conventional notation). However, the engagementmechanisms may also be provided on sides of the pellicle frame 17 whichwill be oriented perpendicular to the scanning direction during use in alithographic apparatus (indicated in FIG. 3 as the x-direction inaccordance with conventional notation).

The protrusions which are received by the engagement mechanisms 50A-Dmay be located on the front surface of the patterning device.Additionally or alternatively, the protrusions may be located on sidesof the patterning device. Protrusions may extend upwardly from sides ofthe patterning device. In such an arrangement the protrusions may eachhave a flattened lateral surface to facilitate secure bonding to a sideof the patterning device.

FIG. 3 depicts four engagement mechanisms 50A-D secured to a pellicleframe 17. Two of the sub-mounts 50A,D are configured to allow formovement in the y-direction (i.e. provide flexibility or compliance inthe y-direction). Two sub-mounts 50B,C are configured to allow formovement in the x-direction (i.e. provide flexibility or compliance inthe x-direction). However, all four sub-mounts 50A-D are configured toallow engagement to be achieved between the sub-mounts and protrusions(not depicted) via movement in the y-direction and thus, as may be seen,all four sub-mounts include engagement arms 80 which extend in they-direction. A possible disadvantage of this configuration is thatsudden deceleration during a y-direction scanning movement could causethe engagement mechanisms 50A-D to slide out of attachment to theprotrusions (due to inertia of the pellicle frame 17). This might occurfor example if there is a ‘crash’ of the mask support structure MT (seeFIG. 1). In an alternative arrangement, all four sub-mounts may includeengagement arms which extend in the x-direction (i.e. the non-scanningdirection). Having the engagement arms all extending in the non-scanningdirection is advantageous because this avoids the possibility of asudden y-direction deceleration causing disengagement of the engagementmechanisms. In general, the engagement arms of each sub-mount may allextend in substantially the same direction.

In order to allow movement/flexibility in the x-direction, arms 62 whichsupport locking members of two of the sub-mounts 50B, C extend in they-direction. These arms are resiliently flexible in the x-direction andthus provide movement/flexibility in the x-direction. Thus, engagementarms 80 of two of the sub-mounts 50B,C extend generally parallel to thearms 62 of that sub-mount. In order to allow movement/flexibility in they-direction, arms 62 which support locking members of the other twosub-mounts 50A,D extend in the x-direction. These arms are resilientlyflexible in the y-direction and thus provide movement/flexibility in they-direction. Thus, engagement arms 80 of two of the sub-mounts 50A,Dextend generally perpendicular to the arms 62 of that sub-mount. Themovement/flexibility which is provided by the sub-mounts 50A-D allowsflexing of the pellicle frame 17 relative to the patterning device MA asneeded when temperature changes occur. This is advantageous because itavoids potentially damaging thermal stresses arising in the pellicleframe 17.

The sub-mounts 50A-D are depicted with tabs 56 which have a differentconfiguration from the tabs 56 depicted in FIG. 5. However, the tabsprovide the same function of facilitating engagement between thesub-mounts 50A-D and the pellicle frame 17. Any suitable configurationof tabs may be used.

FIG. 4 depicts in cross-section one engagement mechanism 50B along witha protrusion 51 which projects from a patterning device MA. Theprotrusion 51, which may be referred to as a stud, may for example beglued to the patterning device MA or may be attached by other bondingmeans (optical contacting, magnetic or van der Waals forces, etc). Theengagement mechanism 50B and the protrusion 51 together form a sub-mount10. The protrusion 51 comprises a distal head 53 located on a shaft 55which extends from a base 57. The base 57 is fixed to the patterningdevice MA for example by using glue. The shaft 55 and distal head 53 maybe cylindrical, or they may have any other suitable cross-sectionalshape.

The sub-mount 10 suspends the pellicle frame 17 relative to thepatterning device MA such that there is a gap G (which may be consideredto be a slit) between the pellicle frame and the patterning device. Thegap G may be maintained by engagement between a cap 66 of the engagementmechanism 50B and the distal head 53 of the protrusion 51 (or by someother movement limiting component). The gap G may be sufficiently wideto allow equalization of pressure between the exterior environment andthe space between the pellicle and the patterning device. The gap G mayalso be sufficiently narrow that it provides a desired restriction ofthe potential route of contamination particles from the exteriorenvironment to the space between the pellicle and the patterning device.The gap G may for example be at least 100 microns in order to allowequalization of pressure between the exterior environment and the spacebetween the pellicle and the patterning device. The gap G may forexample be less than 500 microns, more preferably less than 300 microns.The gap G may for example be between 200 microns and 300 microns.

FIG. 5 depicts the sub-mount 10 of FIG. 4 in more detail. The pellicleframe attached to the engagement mechanism 50B is not depicted in FIG.5. Similarly, the patterning device from which the protrusion 51projects is not depicted in FIG. 5. FIG. 5A shows the sub-mount 10viewed from below and FIG. 5B shows the sub-mount in a perspective viewseen from below.

The engagement mechanism 50B comprises a rectangular outer wall 60 whichis received in an opening in a pellicle frame (see FIG. 3). A pair ofarms 62 extend in the y-direction across a space defined by the outerwall 60. A connecting member 63 extends between distal ends of the arms62. The arms 62 are examples of resilient members. Other resilientmembers may be used. The arms 62 and connecting member 63 together forma generally U-shaped support. A locking member 70 is connected to adistal end of the generally U-shaped support. The locking member 70engages with the protrusion 51 (which may be referred to as a stud)thereby securing the pellicle frame to the patterning device.

The locking member 70 comprises a pair of engagement arms 80 providedwith engagement tabs 81 and further comprises a cap 66. As may be bestseen in FIG. 5B, when the locking member 70 is engaged with theprotrusion 51, the engagement tabs 81 press against an under-surface ofa distal head 53 of the protrusion, and the cap 66 presses against anouter surface of the distal head 53. This pressing of the engagementtabs 81 and cap 66 against the distal head 53 of the protrusion 51secures the engagement mechanism 50B to the protrusion to provide asecure sub-mount 10. This provides a secure connection between thepellicle frame and the patterning device.

The cap 66 and the engagement arms 80 extend from intermediate arms 82a,b. The intermediate arms 82 a,b extend from the connecting member 63and extend in the y-direction back across a space generally defined bythe outer wall 60. A connecting member 83 extends between theintermediate arms 82 a,b. The intermediate arms 82 a,b and connectingmember 83 together form a generally U-shaped support.

Thus, a first generally U-shaped support formed by arms 62 andconnecting member 63 extends in the y-direction across the spacegenerally defined by the outer wall 60, and a second U-shaped supportformed by support arms 82 a,b and connecting member 83 extends backacross that space.

The arms 62 which form the first generally U-shaped support have someflexibility in the x-direction, and this allows some movement in thex-direction of the locking member 70. Thus the sub-mount 10 allows somemovement in the x-direction of a pellicle frame relative to a patterningdevice at the location of that sub-mount. The arms 62 are formed fromresilient material and therefore tend to return to their originalorientations. The sub-mount 10 may be considered to be a kinematicsub-mount. The arms 62 are significantly thicker in the z-direction thanin the x-direction (as may best be seen in FIG. 5B), and as a resultsignificantly less bending of the arms in the z-direction is possiblecompared with bending of the arms in the x-direction. Since the armsextend in the y-direction, they do not provide for significant movementin the y-direction. The arms 62 may thus prevent or substantiallyprevent local movement of a pellicle frame in the y and z-directionswhilst allowing some movement in the x-direction.

The cap 66 extends from the first support arm 82 a, and engagement arms80 extend from the second support arm 82 b. The first support arm 82 ais significantly thicker in the x-direction than the arms 62, and thusdoes allow significant movement in the x-direction relative to the arms62. The second support arm 82 b has a similar thickness to the arms 62in the x-direction, but the connecting member 83 which extends betweenthe intermediate arms 82 a,b inhibits movement of the second support arm82 b in the x-direction because such movement can only occur if thefirst support arm 82 a also moves.

The engagement arms 80 extend from the second support arm 82 b in thegeneral direction of the cap 66. Proximal ends of the engagement arms 80extend along the majority of the second support arm 82 b (therebysubstantially preventing the engagement arms 80 from flexing indirections which are generally parallel to a patterned surface of thepatterning device). The engagement arms 80 taper as they extend in thegeneral direction of the cap 66. Engagement tabs 81 extend inwardly fromdistal ends of the engagement arms 80 to engage with an under-surface ofa distal head 53 of the protrusion 51. Blocks 54 are provided above theengagement tabs 81 and provide actuator receiving surfaces as isexplained further below. The engagement arms 80 are resilientlydeformable in the z-direction. The engagement arms 80 may besufficiently thin that they bend in the z-direction. Additionally oralternatively, some bending in the z-direction of the engagement arms 80may be facilitated by a groove 59 which extends in the y-direction atthe point where the engagement arms 80 connect to the support arm 82 b.

Tabs 56 extend outwardly from the outer wall 60. The tabs may be used tosecure the engagement mechanism 50B to a pellicle frame. This isdepicted in FIG. 3 but with a different configuration of tabs.

FIG. 6 schematically depicts in cross section a pellicle attachmentapparatus 855 which may be used to attach the pellicle 19 to thepellicle frame 17. The pellicle attachment apparatus 855 may correspondwith the pellicle attachment apparatus depicted in FIG. 2. The pellicleframe 17 is supported by a support structure 101. The support structure101 includes a raised portion 102 upon which the pellicle frame 17rests. The pellicle 19 is held by support arms 103 which projectdownwardly from a frame (not depicted). Imaging sensors 105 (e.g.cameras) are provided beneath the support structure 101 and look throughwindows 107 which are provided in an upper surface of the supportstructure. Alignment marks 109 are provided on the windows. Thealignment marks 109 allow the imaging sensors 105 to determine theposition of both the frame 17 and the pellicle 19 (as discussed below inconnection with FIG. 7). Actuators 111 are connected to the supportstructure 101 and are operable to move the support structure 101relative to a base (not depicted). The actuators 111 are configured tomove the support structure 101 in the x, y and z directions (in thisdocument x and y may indicate two orthogonal horizontal directions, andz may indicate the vertical direction). The actuators are alsoconfigured to rotate the support structure 101 about the z-axis. Theactuators 111 allow the support structure 101 to be moved in order toposition the frame 17 relative to the pellicle 19 before the pellicle isattached to the frame.

FIG. 7 schematically depicts part of the pellicle attachment apparatusof FIG. 6 in more detail, including the pellicle 19 and pellicle frame17. The relative positions of the imaging sensor 105, window 107,pellicle frame 17 and pellicle 19 can be seen in FIG. 7. The pellicleframe 17 partially projects over the window 107, and as a result theedge of the frame 17 is visible to the imaging sensor 105. This allowsthe position of the frame 17 to be accurately determined relative to thealignment marks 109 provided on the window 107. The pellicle 19 has aborder 20 around its outer perimeter which is significantly thicker thanthe main portion of the pellicle 19. It is this border 20 which isattached to the pellicle frame 17. In addition it is this border 20which is handled by the support arms 103 (depicted in FIG. 6). As may beseen from FIG. 7, the border 20 projects beyond an inner edge of theframe 17, and thus an inner edge of the border is visible to the imagingsensor 105. This allows the border 20 (and thus the pellicle 19 ingeneral) to be accurately positioned relative to the alignment marks 109in the window 107. This in turn allows the border 20 (and pellicle) tobe accurately positioned relative to the frame 17 (since the frame isaccurately positioned relative to the alignment marks 109 in the window107).

The imaging sensor 105 and window 107 may be located at a cornerposition in the support structure 101, i.e. a position where a corner ofthe frame 17 is located in use. Imaging sensors 105 may be located atopposite corner positions. By seeing opposite corners of the frame 17the imaging sensors 105 allow the position of the frame to be determinedaccurately.

FIG. 8 is a perspective view of a handling system 113 which may be usedto handle the pellicle 19. A handling system with the same configurationmay also be used to handle the pellicle frame 17.

Support arms 103 of the handling system 113 hold the border 20 of thepellicle 19. The support arms are connected by connector arms 115 to ahandling system frame 117. The handling system frame 117 is fixed in thex and y directions but is moveable in the z direction. A vacuum source(not depicted) is connected to a conduit 119 of the handling systemframe via a port 120. The conduit 119 splits into two and travels alongeach arm of the handling system frame 117. Each support arm 103 containsa conduit (not depicted) which terminates at an opening provided in afoot 104 at the bottom of that support arm. Each conduit is connectedvia bellows 121 to the conduit 119 in the handling system frame 117. Inthis way, a vacuum which is applied at the port 120 is connected via theconduit 119 and the bellows 121 to the openings in the feet 104 of thesupport arms 103. When the vacuum is applied it sucks the border 20 ofthe pellicle 19 towards the foot 104 of each support arm 103 and thussecures the border 20 to the support arms. Each foot 104 is dimensionedto receive the border 20 of the pellicle 19 (e.g. has a width whichcorresponds with the width of the border). When the vacuum is removedthe border 20 is no longer sucked towards the feet 104 of the supportarms 103 but instead is released from the support arms.

FIG. 9 is a perspective view of part of the handling system 113 in moredetail, although with connector arms 115 which have a modifiedconfiguration compared with those depicted in FIG. 8. Each connector arm115 comprises a pair of leaf springs 123, the leaf springs extendingfrom the handling system frame 117 to a support arm 103. The leafsprings 123 provide flexibility in the z-direction (i.e. vertical) butprovide little or no flexibility in the x and y directions. This isachieved by the leaf spring being significantly thinner in thez-direction than it is in the x and y directions. The bellows 121 whichare used to communicate the vacuum to the support arms 103 are flexibleand thus permit relative movement of the support arms 103 relative tothe handling system frame 117.

Movement limiting arms 125 project from the support arms 103 towards thehandling system frame 117. Adjustable end stops 127 (e.g. bolts held inthreaded bores) are fixed to the handling system frame 117. Theadjustable end stops 127 limit downward movement of the movementlimiting arms 125 (i.e. movement in the minus z direction). Theadjustable end stops 127 thus prevent downward movement of the pellicle19 beyond a predetermined position.

When a pellicle is to be attached to a pellicle frame, in a first step ahandling system is used to pick up the frame. The handling system (notdepicted) may be generally the same as the handling system describedabove in connection with FIGS. 8 and 9. The foot at the bottom of eachsupport arm may have a size and shape which corresponds with a portionof the frame that will come into contact with the foot.

Once the pellicle frame 17 has been lifted by the handling system, thesupport structure 101 is positioned beneath the pellicle frame. Thepellicle frame 17 is lowered until it is a few millimetres above thesupport structure 101. Referring again to FIGS. 6 and 7, the supportstructure 101 is then moved using the actuators 111 until it isaccurately positioned relative to the pellicle frame 17 (as determinedusing the imaging detectors 105). The pellicle frame 17 is then loweredonto the support structure 101. The vacuum holding the pellicle frame 17to the handling system is then released and the handling system is movedaway from the pellicle frame 17. Glue is then provided on the pellicleframe 17. The glue may be provided at spaced apart locations around theframe (rather than providing glue which extends in a line around theframe).

The pellicle 19 is lifted by the handling system 113 as described above.The support structure 101 (together with the frame 17) is thenpositioned beneath the pellicle 19. The pellicle 19 is lowered using thehandling system 113 until it is a few millimetres above the supportstructure 101. The support structure 101 is then moved using theactuators 111 until it is accurately positioned relative to the pellicleborder 20. The pellicle is then lowered onto the pellicle frame. Oncethe pellicle 19 has been located on the frame 17 the vacuum is releasedfrom the support arms 103, and the support arms 103 are moved away fromthe pellicle 19.

FIG. 10 schematically depicts from above the pellicle 19 in position onthe pellicle frame 17 which in turn is held on the support structure101. FIG. 10 schematically depicts arms 130 which apply downwardpressure to the pellicle border 20 thereby holding the pellicle in placeon the frame 17 whilst curing of the glue attaching the pellicle to thepellicle frame 17 takes place. The glue may be provided at spaced apartlocations on the pellicle frame 17, and the arms 130 may be positionedto apply pressure at the locations at which glue has been provided.

FIG. 11 depicts one of the arms 130 in cross-section. The arm 130comprises a weighted portion 132 which is connected to a support portion134 that extends from a support frame 136. The weighted portion 132includes a projection 138 which is provided with a vertical bore 140.The projection 138 projects into an opening 142 in the support portion134. A pin 144 extends from the top to the bottom of the opening 142 andpasses through the bore 140. Because the pin 144 and bore 140 are bothoriented in a vertical direction (the z direction), the pin and borearrangement allows some vertical (or generally vertical) movement of theweighted portion 132 relative to the support portion 134 of the arm 130.The range of vertical movement of the weighted portion 132 relative tothe support portion 134 is limited by end stops 146 provided at themouth of the opening 142. The end stops are arranged to contact with theprojection 138 and thereby prevent further vertical movement of theweighted portion 132.

A finger 148 extends downwardly from the weighted portion 132 of the arm130. A cap 150 is provided at a bottom end of the finger 148. The cap150 may have a lowermost surface which generally corresponds in sizewith (or is larger than) an area of glue provided on the pellicle frame17. The finger 148 comprises a vertical rod 152 which is secured at anuppermost end to the weighted portion 132 of the arm 130. The verticalrod 152 extends downwardly and passes through an opening 154 provided inthe weighted portion 132. The opening 154 is significantly wider thanthe rod 152 and thus permits some lateral movement of the bottom end ofthe rod to take place (and thus lateral movement of the end of thefinger). This is advantageous because it allows the cap 150 to rest uponthe border 20 of the pellicle 19 without applying significant lateralforces to the pellicle (as could occur if the rod 152 was not free tomove in a lateral direction relative to the weighted portion 132 of thearm 130).

In use, the support frame 136 holds the arms 130 away from the pellicle19 until the arms are needed. The support frame 136 then moves the arms130 downwards until a downwardly projecting finger 148 of the arm comesinto contact with the border 20 of the pellicle 19. Downward motion ofthe support frame 136 ceases before the projection 138 of the weightedportion 132 comes into contact with an upper end stop 146 of the supportportion 134. Thus, the weighted portion 132 rests upon the border 20,pressing on the border 20 via the finger 146, and is not supported bythe support frame 136.

The downward pressure exerted on the border 20 by the weighted portion132 is determined by the weight of the weighted portion. The weightedportion 132 may thus be constructed to have a desired weight in order toapply a desired pressure to the border 20. The weighted portion 132 mayinclude a weight receiving recess 149 into which a weight may be placed.The weighted portion 132 may include any suitable weight receivingreceptacle or projection.

Referring again to FIG. 10, the arms 130 are used to apply pressure atdesired locations around the border 20 of the pellicle 19. The weightedportions 132 of the arms are left in place for a period of timesufficient to allow some curing of the glue between the frame 17 and theborder 20 to take place. The support frame 136 is then moved upwards inorder to remove the weighted arms 132 from the border 20. The frame 17and pellicle 19 (which together may be referred to as a pellicleassembly 16) may then be transferred to an oven in order to further curethe glue.

An embodiment of a pellicle frame attachment apparatus 857 is depictedin FIGS. 12-15. The pellicle frame attachment apparatus 857 maycorrespond with the pellicle frame attachment apparatus shown in FIG. 2.FIG. 12 schematically shows the pellicle frame attachment apparatus 857in cross-section. FIG. 13 shows a partition 862 of the pellicle frameattachment apparatus 857 viewed from above. FIG. 14 is a perspectiveview of a pin 1090, hooked members 1091 and manipulator pins 1092 of thepellicle frame attachment apparatus, which may collectively be referredto as manipulators. The manipulators project through a hole 895 in thepartition 862. FIG. 15 schematically depicts the manner in which thepins 1090, hooked members 1091 and manipulator pins 1092 are capable ofmoving relative to each other.

Referring first to FIG. 12, a pellicle assembly 16 comprises apatterning device MA provided with a pellicle frame 17 and a pellicle(not depicted). The frame 17 is provided with four engagement mechanisms50 which correspond with the engagement mechanisms described furtherabove in connection with FIGS. 3 to 5. Pins 1090 of the pellicle frameattachment apparatus 857 project through holes 895 in a partition 862.The partition 862 may correspond with, or be located on top of, asupport structure 101. The support structure 101 may be the same as thesupport structure 101 which forms part of the pellicle attachmentapparatus (see FIG. 6). Alternatively, the support structure 101 may bedifferent from but may, optionally, have features in common with thesupport structure 101 which forms part of the pellicle attachmentapparatus. Windows 893, 894 are located in the support structure 101,and imaging sensors 105, 106 are located beneath the windows. Alignmentmarks 109 are provided on the windows 893, 894.

An additional support structure 97 is provided at an outer perimeter ofthe pellicle frame attachment apparatus 857. The additional supportstructure may have a fixed position (as depicted), and is referred toherein as the fixed support structure 97. An intermediate supportstructure 98 is provided on top of the fixed support structure 97. Theintermediate support structure 98 extends inwardly from the fixedsupport structure 97 as depicted. The intermediate support structure 98supports both the pellicle frame 17 and the patterning device MA priorto attachment of the pellicle frame to the patterning device. Contacts99 between the intermediate support structure 98 and other entities mayfor example be kinematic connections. The contacts 99 may be providedwith a coating of PEEK.

The pellicle frame attachment apparatus 857 includes actuators 111 whichmay be used to adjust the position of the pellicle assembly 16 in the x,y and z directions and to rotate the pellicle assembly about the zdirection. Two imaging sensors 105 (e.g. cameras), are positioned toview portions of the pellicle (e.g. corners of a border of thepellicle). Two other imaging sensors 106 (only one of which is depictedin FIG. 12) are positioned to view alignment marks provided on thepatterning device MA (which may be a patterning device MA). Alignment oftwo entities using alignment marks is well-known in the art and is notdescribed further here. The actuators 111 and the imaging sensors 105,106 may collectively be referred to as a control system 870.

A gas outlet (not depicted) may be configured to supply gas on thepellicle frame 17 side of the partition 862. The gas may be delivered ata pressure which is higher than a gas pressure on an opposite side ofthe partition.

FIG. 13 depicts the partition 862 in more detail. As may be seen, thepartition 862 is provided with four windows. Two of the windows 893 arepositioned to allow the imaging sensors 106 to view alignment marksprovided on the patterning device MA. The other two windows 894 arepositioned to allow the imaging sensors 105 to view the pellicle frame17 (e.g. to view corners of the pellicle frame). The windows 893, 894may for example be formed from quartz.

The partition 862 is further provided with holes 895, the holes beingpositioned to correspond with the positions of engagement mechanisms 50of the pellicle assembly 16. One of the holes 895 is depicted in moredetail in FIG. 14. The hole 895 is dimensioned to allow a pin 1090 andmanipulator pins 1092 to project through the hole. hooked members 1091project from sides of the hole. In other words, the hooked members 1091are fixed to the partition 862 and project from the partition. The pin1090, hooked members 1091 and manipulator pins 1092 are also depicted inFIGS. 12, 13 and 15.

In use, the pellicle assembly 16 is loaded onto the pellicle frameattachment apparatus 857. It may be transferred to the pellicle frameattachment apparatus 857 without exposing it to contamination. Forexample, the pellicle assembly transport device 881 may be received in aload lock (not depicted) within the pellicle frame attachment apparatus857, and the pellicle assembly 16 may be removed from the transportdevice within the load lock. The pellicle assembly 16 may then betransferred to the controlled environment 857 above the partition 862.

In an embodiment, the pellicle assembly 16 may be manually positionedrelative to the pellicle frame attachment apparatus 857, for exampleusing a handling system as depicted in FIG. 8. The pellicle assembly 16is then placed onto the intermediate support structure 98.

The patterning device MA (with studs 51) may be transferred to thepellicle frame attachment apparatus 857 without exposing it tocontamination. For example, the mask transport device 881 may bereceived in a load lock (not depicted) within the pellicle frameattachment apparatus 857, and the patterning device MA may be removedfrom the transport device within the load lock. The patterning device MAmay then be transferred to the controlled environment 857 above thepartition 862. In an embodiment, the patterning device MA may bemanually positioned relative to the pellicle frame attachment apparatus857, for example using a handling system generally as depicted in FIG.8. The pattering device is then placed onto the intermediate supportstructure 98.

As noted further above, the controlled environment 859 above thepartition 862 may be held at a pressure higher than the pressure beneaththe partition (e.g. by delivering gas above the partition). As will beappreciated from FIGS. 12 to 15, the openings 895 in the partition 862are relatively small, thus limiting the likelihood of contaminationpassing through the openings into the controlled environment. Thislikelihood is further reduced by the higher pressure of the controlledenvironment 859 with respect to the environment in the feed partition862. The higher pressure ensures that air flows downwards through theholes 895, thereby carrying contamination away from the pellicle 19.

When securing the pellicle assembly 16 to the patterning device MA, theimaging sensors 105, 106 are used to monitor the positions of thepellicle assembly relative to the patterning device MA. This occursafter the pellicle frame 17 has been lifted from the intermediatesupport structure 98 by the pins 1090. The position of the pellicleframe 17 is adjusted using the actuators 111. This moves the supportstructure 101 and thus moves the pellicle frame 17 relative to thepatterning device MA. Operation of the actuators 111 may be manual, ormay be controlled by an automated controller. The movement of thesupport structure 101 may continue until the pellicle frame 17 isaligned relative to the patterning device MA.

Once the pellicle frame 17 has been correctly positioned relative to thepatterning device MA, the pins 1090, hooked members 1091 and manipulatorpins 1092 are used to engage the engagement mechanisms 50 to the studs51 which project from the patterning device MA.

The manner in which the pins 1090, hooked members 1091 and manipulatorpins 1092 are capable of moving relative to each other is schematicallyillustrated in FIG. 15. As mentioned above, the hooked members extendfrom the support structure 101 and thus are not capable of movementrelative to the support structure. The support structure itself 101 maybe moved, as explained above, including movement in a generally verticaldirection (z-direction). The manipulator pins 1092 are moveable in agenerally vertical direction (z-direction) by an actuator 320. Themanipulator pins 1092 are both fixed to the actuator 320 and thus bothmove together. The pin 1090 which supports the pellicle frame 17 is notactively moveable relative to the manipulator pins 1092. The pin 1090 isconnected via a spring 322 to the actuator 320. As a result, upward anddownward movement of the actuator 320 will cause corresponding movementof the pin 1090 unless the pin is in contact with the pellicle frame 17.If the pin 1090 is in contact with the pellicle frame 17 then furtherupward movement of the actuator 320 will not cause further upwardmovement of the pin but will instead cause compression of the spring322. Once the spring 322 has been compressed, downward movement of theactuator 320 won't cause downward movement of the pin 1090 until thespring 322 has expanded to a relaxed configuration.

FIGS. 16 and 17 schematically depict the manner in which the engagementmechanism 50 is brought into engagement with the protrusion 51 (whichmay also be referred to as a stud). Both Figures show the engagementmechanism and protrusion in cross-section viewed from one side and alsoviewed from below. Referring first to FIG. 16, the engagement arms 80are pushed away from the cap 66 using manipulator pins (not depicted)which push against distal ends of the engagement arms. As may be seenfrom FIG. 16, there is no contact between the engagement mechanism 50and the protrusion 51 at this point.

The engagement mechanism is moved in the x-direction until the distalhead 53 of the protrusion 51 is located above the engagement tabs 81which project from the engagement arms 80. This movement is achieved bymoving the pellicle frame to which the engagement mechanism 50 is fixedand thus moves all engagement mechanisms in unison.

Once the engagement mechanism 50 is in position the manipulator pinswhich were pushing the engagement arms 80 away from the distal head 53of the protrusion 51 are removed. Since the engagement arms 80 areresilient they move downwards and push against an inner surface of thedistal head 53. The engagement tabs 81 thus press the distal head 53against the cap 66, thereby securing the engagement mechanism 50 to theprotrusion 51. This is depicted in FIG. 17.

It may be desired to remove the pellicle assembly 16 from the patterningdevice MA (e.g. if contamination has been detected on the pellicle).This removal may be performed by the pellicle frame attachment apparatus857. The above sequence is reversed in order to disconnect theengagement mechanism 50 from the protrusion 51.

Operation of the pins 1090, hooked members 1091 and manipulator pins1092 may be manual, automated, or semi-automated.

The pins 1090, hooked members 1091 and manipulator pins 1092 may forexample be formed from steel. Surfaces of the pins 1090, hooked members1091 and manipulator pins 1092 which contact the engagement mechanism 50may be provided with a coating of material such as polyether etherketone (PEEK) or some other robust material. Alternatively, the contactsurfaces may simply be polished surfaces of the pins 1090, hookedmembers 1091 and manipulator pins 1092.

Once the pellicle assembly 16 and patterning device MA have beenconnected together to form a mask assembly 15, the mask assembly may beplaced in a mask assembly transport device 853 for transportation to alithographic apparatus LA (see FIG. 2).

FIGS. 18A-H depict in more detail one manner in which the engagementmechanism 50 may be engaged with the protrusion 51. Referring first toFIG. 18A, a pin 1090 is moved in the z-direction until it touches thecap 66 of the engagement mechanism 50. The pin 1090 is moved further inthe z-direction to lift up the engagement mechanism 50. Since theengagement mechanism is secured to the frame 17 (see FIG. 3) this liftsthe entire pellicle assembly 16. The pin 1090 is one of four pins (seeFIGS. 12 and 13) and the pins are moved in unison. The pellicle assembly16 is thus lifted by the four pins 1090 and is supported by those pins.The position of the pellicle assembly 16 is then adjusted using theactuators 111 (see FIG. 12) until the pellicle assembly is alignedrelative to the patterning device MA.

Referring to FIG. 18B, two hooked members are then moved in thez-direction until their distal ends are beyond an uppermost surface ofthe first support arm 82 a. The hooked members 1091 are then moved inthe x-direction until distal ends of the hooked members are above cornerplates 1089 of the support arm 82 a.

As depicted in FIG. 18C, the hooked members 1091 are then moveddownwards until they come into contact with the corner plates 1089 ofthe support arm 82 a. The pin 1090 and hooked members 1091 together gripthe engagement mechanism 50 to allow subsequent operation of theengagement mechanism.

Referring to FIG. 18D, manipulator pins 1092 are moved in a generallyvertical direction and push against blocks 54 provided at distal ends ofthe engagement arms 80. The manipulator pins 1092 push the engagementarms 80 upwards thereby enlarging a space between the engagement tabs 81and the cap 66. The engagement arms 80 are not bent upwards in FIG. 18Ddue to the limitations of the software used to generate the Figures.

Referring to FIGS. 18E and 18F, the engagement mechanism 50 is thenmoved in the x-direction until the distal end 53 of the protrusion 51 islocated above the cap 66 and is located beneath the engagement tabs 81.

As noted further above, all engagement mechanisms 50A-D are moved inunison via movement of the pins 1090 (see FIG. 3). In an alternativearrangement the patterning device and protrusions 51 may all be movedinstead of moving the pellicle frame. In general, lateral relativemovement between the protrusions and the engagement mechanisms is allthat is required. The direction of lateral movement will depend upon theorientation of the engagement arms 80 (and may for example be they-direction rather than the x-direction).

Referring to FIG. 18F, once the cap 66 is positioned under the distalhead 53 and the engagement tabs 81 are above the distal head 53, themanipulator pins 1092 are retracted. The resilience of the engagementarms 80 is such that they return towards their original positions andthus press the engagement tabs 81 against the distal head 53. Theengagement tabs 81 push the distal head 53 against the cap 66. Thissecures the engagement mechanism 50 to the protrusion 51.

Referring to FIG. 18G, the hooked members 1091 are moved upwards andthen moved in the x-direction until they are located away from thecorner plates 1089 of the support arm 82 a. The hooked members 1091 arethen retracted.

Referring to FIG. 18H, in a final step the pin 1090 is retracted.Referring to FIG. 12, when the pins 1090 are retracted the pellicleframe 17 is no longer supported by the pins but instead is supported byits connection to the protrusions 51 which project from the patterningdevice MA. In other words, the pellicle frame 17 is attached to andsupported by the patterning device MA.

The engagement mechanism 50 is secured to the protrusion 51 and thusprovides a secure sub-mount 10 for the pellicle frame (see FIG. 3). Thepellicle frame is thus securely attached to the patterning device. Thepellicle, pellicle frame and patterning device (which may together bereferred to as a mask assembly) may then be placed in a transport device853 for transportation to a lithographic apparatus LA (see FIG. 2).

The steps depicted in FIGS. 18A-H are reversed in order to detach theengagement mechanism 50 from the protrusion 51 and thereby detach thepellicle frame from the patterning device.

None of the steps via which the engagement mechanism 50 is secured tothe protrusion 51 require any sliding movement between components. Inother words, no rubbing of surfaces against each other in a slidingmotion is required. This is advantageous because such rubbing may beliable to cause unwanted particulate contamination.

An alternative sequence of steps (not depicted) may be used to attachthe engagement mechanism 50 to the protrusion 51. In this alternativesequence the hooked members 1091 are moved into position above theengagement tabs 1089 before the pins are used to raise the pellicleframe. Once the hooked members 1091 are in position the pin 1090 is thenmoved upwards to press against the engagement mechanism. The engagementmechanism is thus gripped by the hooked members 1091 and the pin 1090.The engagement mechanism 50 is then lifted by moving the hooked members1091 and the pin 1090 upwards. The same actions are performed for otherengagement mechanisms, and thus the pellicle assembly is lifted. Thepellicle assembly is then aligned relative to the patterning deviceusing the actuators 101 and imaging sensors 105, 106 (see FIG. 12). Theremaining steps may be as described above with reference to FIGS. 18A-H.

Embodiments of stud attachment and stud removal apparatuses are nowdescribed in connection with FIGS. 19-27.

FIG. 19 schematically depicts in cross-section a stud attachmentapparatus 840 according to an embodiment of the invention. The studattachment apparatus 840 has similarities with the pellicle attachmentapparatus 855 depicted in FIG. 6 and the pellicle frame attachment 857apparatus depicted in FIG. 12. Parts of the stud attachment apparatus840 may correspond with parts of those other apparatuses.

The stud attachment apparatus 840 comprises a support structure 101 andstud manipulators 1100 configured to move protrusions 51 (which may alsobe referred to as studs) vertically such that they come into contactwith the patterning device. Windows 107, 108 are provided in the supportstructure 101 and imaging sensors 105, 106 (e.g. cameras) are positionedto look through the windows towards the patterning device MA. Alignmentmarks 109 are provided on the windows and may be used to align thesupport structure 101 relative to the patterning device MA. Actuators111 are provided to move the support structure 101, and thus to movestuds 51 which are held by the support structure 101. The actuators 111are capable of moving the support structure in the x, y and z directionsand are also capable of rotating the support structure about the zdirection. The actuators 111 may be automated, manual or semi-automated(i.e. partially automated and partially manual). The stud attachmentapparatus 840 further comprises an additional support structure 97 whichis configured to support the patterning device MA. This additionalsupport structure may be fixed, and is referred to herein as the fixedsupport structure 97.

In use, glue is provided on the base of each stud 51 whilst the studsare being held by the support structure. The patterning device MA isthen placed onto the fixed support structure 97, such that thepatterning device MA is positioned a few millimeters above the supportstructure 101. The actuators 111 are used to move the support structure101 until alignment marks 109 provided in the windows 107, 108 arealigned with alignment marks provided on the patterning device MA. Thestuds 51 are held by the stud manipulators 1100 and have fixed positionsin the x and y directions relative to the support structure 101. Theseparation between the studs 51 (of which there may be four in practice)is a fixed predetermined separation. The separation between the studs 51corresponds with the separation between the engagement members 50A-Dprovided on a pellicle frame 17 (see FIG. 3) which will be attached tothe patterning device MA.

Once the support structure 101 has been positioned correctly relative tothe patterning device MA, the support structure is moved upwards andcloser to the patterning device. The stud manipulators 1100 are thenused to move the studs 51 upwards from a position in which the bases ofthe studs do not contact the patterning device MA to a position in whichthe bases of the studs press against the patterning device. Heaters arethen used to heat the studs 51 in order to promote curing of the glue atan interface between the bases of the studs 51 and the patterning deviceMA.

FIG. 20 depicts the stud attachment apparatus 840 in a partiallytransparent perspective view. A partition 842 is depicted whichseparates the actuators (not visible) from a controlled environment inwhich the patterning device is provided. The actuators are provided in abox 843 located beneath the partition 842. The imaging sensors 105, 106which form part of an alignment measurement system 844 for aligning thestuds to the patterning device are also provided beneath the partition842 (as are other parts of the alignment system).

Also depicted in FIG. 20 is a lift unit 845 which may be used to raiseand lower a mask support which is used to put the patterning device ontothe fixed support 97 (see FIG. 19). The mask support may comprise ahousing 879, which will form part of a mask transport device 880(described further above in connection with FIG. 2). The patterningdevice (not visible) and housing 879, together with the lift unit 845may be provided in a controlled environment (walls of which are notdepicted). The controlled environment may be held at a pressure which ishigher than the pressure on an opposite side of the partition 842, suchthat contamination is inhibited from flowing through openings in thepartition and into the controlled environment. The controlledenvironment may be provided with a flow of gas from an inlet and mayinclude an outlet through which gas may flow (the flow beingsufficiently constrained that the pressure in the controlled environmentcan be held at a level which is higher than the pressure below thepartition 842). This flow of gas may help to remove contaminants fromthe controlled environment. A filter which collects contaminants may beprovided at the gas inlet to prevent or inhibit contaminants fromentering the controlled environment.

Points at which the mask comes into contact with the stud attachmentapparatus 840 may be provided with a coating of PEEK or some otherrobust material. Similarly, points at which the mask comes into contactwith the housing 879 may be provided with a coating of PEEK or someother robust material.

Part of the stud attachment apparatus 840 is depicted in more detail inFIG. 21. A stud manipulator 1100 is depicted together with a stud 51 anda patterning device MA (e.g. a mask). Also depicted is a partition 842which separates an environment in which the patterning device isprovided from an environment in which the stud manipulator 1100 isprovided. The stud manipulator 1100 comprises a cup 1102 which isdimensioned to receive a stud 51 (which may also be referred to as aprotrusion), such that a bottom face of the stud 51 is facing outwardsfrom the cup. The cup 1102 may, for example, be formed from PEEK or someother robust material. The cup 1102 is held in a manipulator head 1104which in turn is supported on a manipulator body 1106. A spring 1108 isreceived against a flange 1109 provided on the manipulator body andbiases the manipulator head 1104 and the stud 51 upwards. Alignment ofthe stud 51 relative to the mask is achieved using the imaging sensors105, 106 and actuators 111 depicted in FIG. 19. When the actuators havealigned the studs 51 to the patterning device MA, the stud manipulator1100 is moved upwards to press the studs against the patterning device.The stud manipulator 1100 is moved upwards by an actuator (not depicted)which moves all four stud manipulators upwards at the same time. Thespring 1108 is compressed when the stud manipulator 1100 presses thestud 51 against the patterning device MA. The spring 1108 partiallydetermines the force with which the stud 51 is pressed against thepatterning device MA. A weaker spring will reduce the force with whichthe stud is pressed against the patterning device, whereas a strongerspring will increase the force which the stud is pressed against thepatterning device. Thus, the force with which the stud 51 is pressedagainst the patterning device MA is selectable (at least in part) viaselection of a spring 1108 with a desired strength. The spring 1108 mayfor example be pre-loaded with a force which pushes the stud manipulator1100 and stud 51 upwards. The force of the pre-load may for example beless than 5N.

The stud manipulator 1100 pushes the stud 51 against the patterningdevice MA and thereby allows the stud to be secured to the mask. Asnoted above, the stud may be provided with glue or adhesive on its base,and the stud manipulator 1100 may press the stud 51 against thepatterning device MA until the glue or adhesive has hardened. Once thishas taken place, the stud manipulator 1100 may be moved away from thepatterning device MA (and/or the patterning device may be moved awayfrom the stud manipulator 1100).

In an embodiment, the stud manipulator 1100 may include a heater 1111which is configured to heat the stud 51. The heater 1111 may be in theform of an electrical heater (e.g. a resistive electrical heater). Whenthe stud 51 is being held against the patterning device MA the heater1111 is used to heat the stud. The localized heating of the stud 51provided by the heater 1111 is advantageous because it acceleratescuring of the glue or adhesive. This increases the throughput of thestud attachment apparatus 840. The curing provided by heating the stud51 may be pre-curing or may be full curing. Where pre-curing is used thepatterning device MA and studs 51 may be transferred to an oven forcuring. Where heating the stud 51 provides full curing there is no needto transfer the mask and studs to an oven. This is advantageous becausethe oven may be a source of contamination particles.

In an embodiment, the stud manipulator 1100 may include an actuator (notdepicted) which is operative to press the stud 51 against the patterningdevice MA (in addition to, or instead of, the spring 1108). The actuatormay in addition move the cup 1102 away from the stud 51 once the studhas been fixed to the patterning device MA.

A seal 1112 extends around an outer perimeter of the manipulator head1104. The seal 1112 is most clearly seen in FIG. 22, which depicts partof the stud manipulator 1100 as viewed from above (looking through thepatterning device MA which is generally transparent in FIG. 22 for easeof illustration). As may be seen from FIG. 22, in the illustratedembodiment the seal 1112 is annular in shape. However, the seal may haveany suitable shape.

Referring again to FIG. 21, the seal 1112 is formed from resilientmaterial (e.g. PEEK) and projects above the partition 842 and above thestud 51. Thus, when the stud is pressed against the patterning device MAthe seal 1112 is pushed downwards. The resilient nature of the seal 1112means that the seal presses against the patterning device MA and therebyforms a seal against the patterning device. This seals the portion ofthe patterning device MA within the perimeter of the seal 1112 andisolates it from the portion of the patterning device MA which isoutside of the perimeter of the seal.

Gas extraction channels 1114 are provided in the manipulator head 1104,the gas extraction channels extending away from outer face of themanipulator head. An additional gas extraction route is provided by anannular space 1115 around the manipulator head 1104. A gas deliverychannel 1118 is provided on one side of the seal 1112 and allows gas tobe delivered to the area of the patterning device MA which is locatedwithin the seal. This is schematically depicted by arrows in FIG. 21.The gas is extracted via the gas extraction channels 1114 in themanipulator head and the annular space 1115 around the manipulator head.The gas extraction channels 1114 are distributed around the manipulatorhead 1104, as is best seen in FIG. 22. A flow of gas is provided whichwill transport contaminants out of the gas extraction channels 1114 andthe annular space 1115 and thereby prevent those contaminants adheringto the surface of the patterning device MA. The contamination may forexample be particulates derived from the glue provided on the stud 51 orchemical vapour from the glue. Chemical vapour may in particular begenerated when the glue is heated for curing. Removing contaminationusing the gas glow is advantageous because, as is explained elsewhere,particulates or other contamination on the surface of the patterningdevice MA may cause errors in a pattern projected on to a substrate by alithographic apparatus. The gas may, for example, be air.

In an embodiment the seal 1112 may be a complete seal, i.e. no gas flowspast the seal. In an alternative embodiment, the seal 1112 may form anincomplete seal against the patterning device MA, such that some gas canflow between the seal and the mask. This may be referred to as a leakageseal (i.e. the seal 1112 is a leakage seal). The seal 1112 may forexample not make contact with the patterning device, such that there isa gap between the seal and the patterning device. The pressure of thegas within the seal may be lower than the pressure of gas outside of theseal, and as a result gas will flow from outside the seal to inside theseal and then out through the gas extraction channels 1114 and theannular space 1115. This is advantageous because contamination particleswill be transported by the flow of gas from an area of the patterningdevice MA which is outside of the seal 1112, pass through the seal, andflow out of the extraction channels 1114. A further advantage of theleakage seal configuration is that avoiding contact between the seal1112 and the patterning device MA prevents contamination beingtransferred from the seal to the patterning device.

FIG. 23 is a perspective view of four studs 51 provided on the supportstructure 101, each stud being surrounded by a seal 1112. Each seal 1112is held on a seal support plate 1113 which is secured to the supportstructure 101. Also shown in FIG. 23 are two windows 108 through whichimaging sensors 106 (see FIG. 19) may view the patterning device MA (notdepicted).

Each seal support plate 1113 is removable along with an associated seal1112 from the support structure 101 (e.g. to allow replacement of a wornseal). FIG. 24 depicts one seal support plate 1113 and seal 1112 removedfrom the support structure 101. As may be seen, positioning pins 1120extend upwards from the support structure 101. These positioning pins1120 are received in holes (one of which is visible in FIG. 21) in theseal support plate 1113, and thereby ensure that the seal support plateis correctly positioned on the support structure 101.

Retaining arms 1122 extend from a block 1124. The retaining arms 1122are located over the seal support plate 1113 and press against pins 1126which extend upwards from the support structure 101. The retaining arms1122 are resiliently biased against the pins 1126 and press against thepins 1126, thereby securely holding the seal support plate 1113 in placeon the support structure. The resilient retaining arms 1122 can bemanually disengaged from the pins 1126 by moving opposing arms towardseach other, thereby allowing the seal support plate 1113 (and seal 1112)to be removed.

Only the studs 51 (and the seal 1112 if a leakage seal is not used) comeinto contact with the patterning device. The stud manipulator 1100 isflexibly connected to the support structure 101 to allow the studmanipulator to move relative to the support structure when the stud 51is being pressed onto the patterning device MA. This flexible connectionis provided via the spring 1108. As a result, when the stud 51 ispressed against the patterning device MA, the stud manipulator 1100 maymove relative to the support structure 101. This is advantageous becauseit avoids significant lateral forces being applied at the interfacebetween the stud 51 and the patterning device MA, thereby avoiding forexample sliding movement of the stud over the surface of the patterningdevice (such movement would generate contamination and is undesirable).

A kinematic connection is provided between the stud manipulator 1100 andthe support structure 101. The kinematic connection is such that thestud manipulator 1100 can press against the support structure when thestud 51 is not in contact with the patterning device, but allows thestud manipulator to disconnect easily from the support structure 101when the stud 51 contacts the patterning device. Referring again to FIG.24, three protrusions 1130 with rounded heads project from the studmanipulator 1100 and are distributed around the stud manipulator. One ofthe three protrusions 1130 is visible in FIG. 21. The protrusions 1130engage with an angled inner surface 1132 of the seal support plate 1113.The angled inner surface 1132 is generally flat, whereas, as mentionedabove, the protrusion 1130 has a rounded upper surface. This combinationof surfaces is advantageous because it provides a very small contactarea between the protrusion 1130 and the angled inner surface 1132. Theother two protrusions contact angled inner surfaces of the seal supportplate in the same manner.

In use, when the stud 51 is not in contact with the patterning device MAthe spring 1108 presses the protrusions 1130 against the angled innersurface 1132 of the seal support plate 1113. This provides a connectionbetween the stud manipulator 1100 and the support structure 101. Theconnection may be a kinematic connection. When the stud 51 is pressedagainst the patterning device MA the spring 1108 is compressed therebymoving the protrusions 1130 away from the angled inner surfaces 1132 ofthe seal support structure 101. The three protrusions 1130 might not allseparate from the angled inner surfaces 1132 at exactly the same time,for example if there is a relative tilt between the patterning device MAand the support structure 101. Instead, one will separate followed by asecond and then by a third. The kinematic connection allows this serialseparation to take place and allows the stud 51 to remain substantiallyperpendicular to the patterning device MA. In other words, the kinematicconnection avoids forcing the stud 51 to have an orientation which isdetermined by the support structure 101 and instead allows the stud tohave an orientation which is determined by the patterning device MA.

It may be desired to remove the studs 51 from the patterning device MA.This removal may be performed using a stud removal apparatus. The studremoval apparatus may have a form which generally corresponds with thestud attachment apparatus 840 (e.g. as schematically depicted in FIG.19). For example, the stud removal apparatus may include a partitionwhich separates a controlled environment in which the patterning deviceMA is held during stud removal from stud removers and other components.The controlled environment may have a higher pressure than other partsof the apparatus. The stud removal tool may for example comprise studremovers in a configuration which corresponds with that shown in FIG.19. Since relatively coarse alignment of the stud removers to the studs51 is sufficient to allow removal to be achieved, in an embodiment theimaging sensors 105, 106 and windows 107, 108 may be absent from thestud removal apparatus. Alignment of the heaters and actuators to thestuds may be performed using a manual, semi-automated or automatedsystem.

FIG. 25 is a perspective view of a stud remover 1149 which forms part ofa stud removal apparatus according to an embodiment of the invention.The stud remover 1149 comprises a stud gripper 1154 connected to asupport plate 1155. A weight 1157 extends downwardly from the studgripper 1154. A pair of leaf springs 1159 extend downwardly from thesupport plate 1155 and are configured to allow movement of the studgripper 1154 in the x-direction (the leaf springs allow movement in agenerally vertical direction).

An actuator 1161 is connected to a flange 1163 which projects downwardsfrom the support plate 1155. The actuator includes an arm 1164 whichpasses through an opening in one of the leaf springs 1159 and connectsagainst a hooked member 1165 that is in contact with the weight 1157. Aridge and groove connection 1175 between the hooked member 1165 and theweight 1157 is provided which allows the weight to move verticallyrelative to the hooked member but prevents relative movement of thehooked member and the weight in the x and y directions. Thus, moving thearm 1163 in the x-direction using the actuator 1161 will cause thehooked member 1165 and the weight 1157 to move in the x-direction.

A second pair of leaf springs 1167 (only one of which is visible in FIG.25) allows movement of the stud gripper 1154 in the y-direction. Noy-direction actuator is provided. Instead, some passive movement in they-direction may occur as the stud moves into the stud gripper 1154 (asexplained below).

An actuator 1169 is located beneath the hooked member 1165 which isconnected via the ridge and groove connection 1175 to the weight 1157(the weight in turn being connected to the stud gripper 1154. Theactuator 1169 is operable to move the stud gripper 1154 in the verticaldirection (in this case denoted as the z-direction).

Thus, movement of the stud gripper 1154 in the x, y and z directions isprovided for by the stud remover 1149.

The weight 1157 may for example be at least 1kg. The weight may forexample be around 3kg.

A receptacle 1173 is provided adjacent to the z-direction actuator 1169and is configured to receive studs which have been removed frompatterning devices.

FIGS. 26 and 27 depict in perspective view and in cross-section part ofthe stud remover 1149 in more detail. FIG. 27 also includes a stud 51and a patterning device MA (e.g. mask). The stud gripper 1154 comprisesa pair of opposed flanges 1156 which extend towards each other toestablish a gap which is wider than a neck of the stud 51 but narrowerthan a distal head 853 of the stud. Below the opposed flanges 1156,recesses 1158 are provided which are wider than the distal head of thestud 51 and can thus receive the distal head of the stud. The distalhead of the stud 51 is not clearly visible in FIGS. 26 and 27 becausethe head extends into and out of the plane of the figures. The recesses1158 and opposed flanges 1156 flare outwardly at one end of the studgripper 1154.

The stud remover 1149 includes a heater 1188 which is located beneaththe stud gripper 1154. The heater is an electrical heater, e.g. aresistive heater, and is configured to locally apply heat to the studgripper 1154. The stud remover further comprises a pusher arm 1200 whichis connected to an actuator 1202. The pusher arm 1200 is configured topush the stud 51, once removed from the patterning device MA, into achute 1204. The chute 1204 leads to the receptacle 1173 (see FIG. 25).

A wire 1206 extends downwards from the heater 1188 and is connected tothe weight 1157 (see FIG. 25).

In use, the actuator stud gripper 1154 is initially in a position whichis to the left of the stud and does not project above a partition 1142of the apparatus. The stud gripper 1154 is then moved upwards using thevertical actuator 1169 (see FIG. 25) to the position shown in FIG. 27.The stud gripper is thus adjacent to but not touching the patterningdevice MA. The x-direction actuator 1161 (see FIG. 25) then moves thestud gripper 1154 in the x-direction such that the distal head 853 ofthe stud 51 enters the stud gripper via the flared ends thereof and isthen located in the non-flared portion (as depicted in FIG. 28). Thismay involve some passive movement of the stud griper 1154 in they-direction. The vertical actuator 1169 is then moved downwards suchthat the support plate 1155 no longer supports the stud gripper 1154,the stud gripper instead being pulled downwards by the weight 1157. Heatis delivered to the stud 51 from the heater 1188 via the stud gripper1154 in order to melt the glue or adhesive which secures the stud to thepatterning device MA. Once the glue or adhesive has melted the stud 51becomes detached from the patterning device MA. The stud 51 movesdownwards due to the weight that is pulling it downwards.

The pusher arm 1200 is then moved in the x-direction as depicted in FIG.29. The pushes the stud 51 from the stud gripper 1154 into the chute1204. The stud then falls into the receptacle 1173. The stud 51 is shownin three positions in FIG. 29 in order to illustrate movement of thestud.

The above process is performed for each stud 51 on the patterning deviceMA. The studs may be removed in series, i.e. one after another.Alternatively, the studs may all be removed together. An advantage ofremoving the studs in series is that the force being applied to thepatterning device is limited to the force needed to remove one stud.This in turn limits the force applied to supports which support thepatterning device, thereby minimizing the risk of damage to thosesupports (and also minimizing the risk of damage to the patterningdevice).

As noted above, a partition 1142 separates the majority of the studremoval apparatus from a controlled environment in which the patterningdevice MA is provided. However, no seal extends around an area of thepatterning device MA on which the stud 51 is provided. A seal wouldprovide little benefit because the patterning device MA will be cleanedafter the stud 51 has been removed, and thus addition of contaminationto the patterning device during stud removal does not pose a significantproblem. A seal may be provided if desired (e.g. a leakage seal).

The stud removal apparatus may further comprise additional stud grippers1154 and associated elements. For example, four stud grippers and otherelements may be provided, one for each stud on the patterning device MA.The stud removal apparatus may generally correspond in form with thestud attachment apparatus 840 depicted in FIG. 21. For example,actuators may be used to adjust the positions of the stud grippers inthe x, y, Z and Rz directions. The actuators may be automated, manual orsemi-automated (i.e. partially automated and partially manual). Thepartition 1142 may separate the actuators from a controlled environmentin which the mask is provided. The actuators may be provided in a boxlocated beneath the partition 1142. Alignment measurement systems mayalso be provided beneath the partition 842. The alignment measurementsystems may for example comprise imaging systems which are used toensure that the stud grippers 1154 are positioned at correct locationsbefore they engage with the studs 51.

Points at which the mask comes into contact with the stud removalapparatus 1150 may be provided with a coating of PEEK or some otherrobust material. Similarly, points at which the mask comes into contactwith the housing may be provided with a coating of PEEK or some otherrobust material.

The stud attachment apparatus 840 and stud removal apparatus 1150 may beprovided as a single apparatus or may be provided as separateapparatuses.

A lift unit 845 and housing are depicted only in FIG. 20, and are shownas part of the stud attachment apparatus 840. However, a lift unit maysimilarly be provided as part of a pellicle frame attachment and/orremoval apparatus and/or may similarly be provided as part of a studremoval apparatus. The lift unit may be configured to raise and lower ahousing which may form part of a mask transport device. A patterningdevice (e.g. a mask) may be held by the housing. The mask, housing andlift unit may be provided in a controlled environment.

In an embodiment, instead of using a weight to remove a stud 51 from thepatterning device MA an actuator may be used to apply downward force tothe stud. The actuator may for example be a Lorentz actuator. TheLorentz actuator may be configured to pull the studs in the z-directiononly.

In an embodiment, instead of heating the stud 51 the patterning deviceMA may be heated (e.g. using a heater located above the patterningdevice). An advantage of this approach is that glue will tend to breakat its interface with the patterning device, thereby leavingsignificantly less residual glue on the patterning device once the studhas been removed.

In an embodiment, instead of heating the glue to melt it the glue may bedissolved via application of a suitable solvent.

Glue may be cleaned from the patterning device MA using a cleaningapparatus. The cleaning apparatus may form part of the stud removalapparatus, or may be provided as a separate apparatus. The patterningdevice MA may be placed into a sealed box for transportation to acleaning apparatus. The cleaning apparatus may be configured to removecontamination from the mask (which may include removing glue from themask).

Although some embodiments of the invention are described with referenceto studs, where the context allows embodiments of the invention may useany form of protrusion.

Although in the described embodiment the frame 17 and mountings 50 areattached to each other before the pellicle 19 is attached to the frame,attachment of these elements may take place in any suitable order. Forexample, the frame 17 and pellicle 19 may be secured together, followingwhich the mountings 50 may be attached the frame. The mountings 50 maybeattached to the frame 17 using an attachment apparatus which generallycorresponds with the pellicle attachment apparatus 855.

References to a mask in this document may be interpreted as referencesto a patterning device (a mask is an example of a patterning device).

References to glue in this document may be interpreted as referring toadhesive in general.

Although specific reference may be made in this text to embodiments ofthe invention in the context of a lithographic apparatus, embodiments ofthe invention may be used in other apparatus. Embodiments of theinvention may form part of a mask inspection apparatus, a metrologyapparatus, or any apparatus that measures or processes an object such asa wafer (or other substrate) or mask (or other patterning device). Theseapparatus may be generally referred to as lithographic tools. Such alithographic tool may use vacuum conditions or ambient (non-vacuum)conditions.

The term “EUV radiation” may be considered to encompass electromagneticradiation having a wavelength within the range of 4-20 nm, for examplewithin the range of 13-14 nm. EUV radiation may have a wavelength ofless than 10 nm, for example within the range of 4-10 nm such as 6.7 nmor 6.8 nm.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications. Possible other applications include the manufactureof integrated optical systems, guidance and detection patterns formagnetic domain memories, flat-panel displays, liquid-crystal displays(LCDs), thin-film magnetic heads, etc.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The descriptions above are intended to beillustrative, not limiting. Thus it will be apparent to one skilled inthe art that modifications may be made to the invention as describedwithout departing from the scope of the claims set out below.

1. A stud removal apparatus, comprising: a support structure configuredto hold a patterning device; a stud gripper configured to receive andretain a distal head of a stud projecting from the patterning device;actuators configured to move the stud gripper relative to the stud andpatterning device; and a heater.
 2. The stud removal apparatus of claim1, wherein the stud gripper comprises a pair of flanges with aseparation that is wider than a neck of the stud and narrower than adistal head of the stud.
 3. The stud removal apparatus of claim 1, thestud removal apparatus further comprises a weight that is connected tothe stud gripper and pulls downwardly on the stud gripper.
 4. The studremoval apparatus of claim 1, wherein the stud removal apparatus furthercomprises a pusher arm that is moveable in a generally horizontaldirection relative to the stud gripper, the pusher arm being configuredto push the stud out of the stud gripper after it has been removed froma patterning device.
 5. The stud removal apparatus of claim 4, whereinthe stud removal apparatus further comprises a chute configured to guidethe stud after it has been pushed out of the stud gripper.
 6. The studremoval apparatus of claim 5, wherein the stud removal apparatus furthercomprises a stud receptacle located at an outlet of the chute.
 7. Amethod of removing a stud from a patterning device, the methodcomprising: supporting the patterning device using a support, with thepatterning device being oriented such that the stud projects downwardlyfrom the patterning device; moving a stud gripper relative to the studand thereby receiving and retaining a distal head of the stud; heatingthe stud gripper and thereby heating the stud to melt glue locatedbetween the stud and the patterning device; and pulling the studdownwards using the stud gripper such that the stud separates from thepatterning device when the glue melts.
 8. The method of claim 7, whereinthe stud is pulled downwards by a weight that is connected to the studgripper and pulls downwardly on the stud gripper.
 9. The method of claim7, further comprising using a pusher arm to push the stud out of thestud gripper after it has been removed from a patterning device.
 10. Themethod of claim 9, further comprising using a chute to direct the studto a stud receptacle.
 11. A method of attaching a pellicle to a pellicleframe, the method comprising: using a pellicle frame handling system toplace the pellicle frame on a support structure; applying glue to thepellicle frame; holding a pellicle above the pellicle frame using apellicle handling system; aligning the pellicle frame and the pellicle;and placing the pellicle onto the pellicle frame.
 12. The method ofclaim 11, wherein alignment of the pellicle frame and the pellicle isachieved by moving the support structure that supports the pellicleframe.
 13. The method of claim 11, further comprising pressingdownwardly onto the pellicle using arms, thereby holding the pellicle onthe pellicle frame during curing of the glue.
 14. The method of claim13, wherein the glue is provided at spaced apart locations and whereinan arm presses down onto the pellicle at each spaced apart location 15.A method of attaching a pellicle assembly to a patterning device, thepellicle assembly comprising a pellicle frame and a pellicle, the methodcomprising: placing the pellicle assembly on a first part of the supportstructure; placing the patterning device on a second part of the supportstructure, with studs of the patterning device facing towards thepellicle assembly; lifting the pellicle assembly from the supportstructure then moving the pellicle assembly to align it relative to thepatterning device; and using manipulators to operate engagementmechanisms of sub-mounts provided on the pellicle frame, themanipulators engaging the engagement mechanisms with the studsprojecting from the patterning device.
 16. The method of claim 15,wherein the manipulators comprise hooked arms and manipulator pins thatconfigured to move engagement arms of each engagement mechanism relativeto support arms of each engagement mechanism in order to create space toreceive a distal head of one of the studs.
 17. The method of claim 16,wherein the hooked arms hold the support arm of the engagement mechanismwhile the manipulator pins push engagement arms of the engagementmechanism upwards.
 18. A method of attaching studs to a patterningdevice, the method comprising: placing the studs in stud manipulatorsprovided on a support structure; applying glue to the studs; placing thepatterning device above the studs and with a patterned surface facingdownwards; and moving the stud manipulators upwards to move the studsinto contact with the patterning device.
 19. The method of claim 18,wherein the method further comprises heating the studs using heaters inthe stud manipulators in order to cure the glue.
 20. The method of claim18, wherein a seal is provided around each stud manipulator and whereingas is delivered to the stud manipulator and then removed from the studmanipulator in order to carry contamination away from the vicinity ofthe seal.